Ha no worries, me too
I think basically it comes from a couple of different things.
First off an outdated one - when all you could get in the UK were forward facing seats, people said keep them in their infant carrier as long as you possibly can, to avoid forward facing too soon - this obviously doesn't apply if you're moving to a rear facing seat.
Then there's an argument about recline - basically the recline in infant seats is much more than the recline in next stage seats, whether you're talking old-fashioned forward facing seats, or the Nordic style seats which used to start at 9kg, like Axkid Minikid. Actually, even Minikid is sort of an exception here because it doesn't have the 9kg minimum, but most seats of that type did, and as you know with the Minikid, it's really not suitable from birth - they need to be tall enough and also the angle is much more upright, it's really designed for toddlers or at the least an older baby who is sitting well by themselves. So there's an argument that just because your baby is 9kg and the seat is rear facing, it's not a good idea to use a seat like that upright when they are only 6 months old or so. This is a bit of a niche one which you'd basically hear in some Northern European countries where they have this very big thing about babies' backs neeing the correct support until 9-10 months when they can sit on their own and not sitting them up too early as they say it causes scoliosis (which is unlikely, I think).
Anyway, that one is actually outdated as well - you don't get those seats which start at 9kg any more. The majority of the seats on the market these days are combo like the Graco which can do from birth (theoretically) up to 18kg/105cm so they recline perfectly fine for a 6 month old, even though sometimes those seats don't give a great fit for a tiny baby (under 3-4 months). And the most modern seats like the Minikid 4, those go from 61cm so they are designed for a baby who can sit with support and do have more recline compared to the older Minikid.
So then the last one which I think is probably what people say now - basically what they mean is that the infant stage of car seat, it really doesn't matter hugely which one you get because they all tend to do really well in independent testing like the ADAC tests. It's probably because they all have a very similar design and the design hasn't changed hugely since the late 1990s - we see the same belt path, the same harness style and similar shape of seat. It just works really well. The only thing that has significantly changed today is the inserts and the use of a headrest, plus much deeper side impact protection - but even the deep side wings have been standard for about 10-15 years. In terms of actual crash protection, you can't get much better than this for younger babies - they are easy to protect because they are small (a larger weight is more unwieldy for rear facing, and forward facing is less protective) and the seats have to be rear facing by law and they all have this same belt path with the anti-rebound (or a base with a support leg).
Even seats from companies like Team Tex/Nania and Cosatto where their other car seats in other categories haven't done very well in the ADAC tests tend to do fine in the infant carrier category. So that's what people mean when they say the infant stage is "safer" - it's not really that there's something inherently safer about those seats, it's more that the design of them is all very similar and doesn't tend to go wrong very often. Whereas when you're choosing a seat for the second stage, it's not so true that you can go for anything - there is much more variance in the quality and crash safety performance. (HBBs are in between - there are some differences in performamce, they don't matter as much as in the toddler stage).
This all gets lost in translation though and people say stuff like the infant carriers "are tested to the same standard" which doesn't mean anything, all seats are tested to the same standards, or even "tested to a higher standard" which is definitely a misunderstanding.
The reality is probably just that toddler seats have the hardest job of all because you have to restrain this fairly heavy, large child within the seat itself AND you have to restrain the seat to the car, and in doing both of those things there is a much wider margin for error. Infant carriers are easy to get right because infants are light and not difficult to restrain, HBBs are easy to get right because the seat is mostly a pre-crash belt positioner, with the seatbelt doing most of the work. Toddler seats are hard to do well, so you should pick a company who have a good track record. This Graco is Joie and they are good. Much better RF than FF, but you want to use it rear facing anyway, so no problem.