It was about well before then, people were throwing it about as advice in 2009 when DS1 was weaning, probably before then too, but I have heard of that FB group. TBH they give some quite dangerous advice (e.g. if you have spoon fed once at 8 months you must totally drop all solids and restart offering one item at a time - this is BONKERS and totally unnecessary, potentially even harmful).
Beware militant FB groups. Some people hear advice, ignore/forget/don't notice the reasoning behind it and adopt it as a kind of badge of what a super parent they are and then go and insist it, as though it was one size fits all, in an extremely bullying manner. In these kinds of echo chamber groups often the same posters will go around with their pet beliefs and brigade everyone else and it becomes a bit oneupmanship, soon advice not to start until 6 months becomes distorted into it's best to start later, so I didn't start until 8 months, 9 months, my child is still fully breastfed age nine or whatever - and because they are an echo chamber with other people repeating the same views it can lend an air of authority.
If you join parenting related FB groups I would recommend to stick with general, preferably local ones, if you join advice related ones make sure you pick one which is staffed by actual experts and check their credentials - often these groups have stricter posting criteria which can be a bit of a pain.
Beware one size fits all advice. Usually there is nuance. Always ask for the reasoning why and if something doesn't make sense explore it for yourself. If in doubt refer back to advice bodies you trust e.g. NHS (whose advice must be evidence based).
Is Aitch's weaning forum still about? :o That was ace! And no weirdness about unaided sitting nor militancy about spoons.