There are some big red flags there, including struggling with single words rather than in context. Guessing is very much part of the dyslexic strategy for reading. For a bright child, it's surprisingly effective! They don't seem to even realise they're doing it: it's just what they do when they read.
The even more telling thing will be if you show him a list of phonetically plausible but made up words, and see how he gets on with those (like 'temat', 'slig', 'gorol'). Do tell him they're made up!
One of the tests they do in a dyslexia assessment is time how quickly they read a list of made up words versus real words. For a child who can read phonetically, it isn't too big a challenge. But a child who relies heavily on memorised 'pictures' of whole words (another dyslexic strategy) will slow right down and struggle.
Dyslexia doesn't necessarily come with behavioural problems or difficulty concentrating. A child who has ASD or ADD does have a higher probability of also having dyslexia, but dyslexia can absolutely stand alone. In fact, you may find a dyslexic child has learned to focus and concentrate really hard because they have to! A fidget toy is the one thing I'd suggest trying. Difficulty with organisation does seem to be part of dyslexia though. You might not see it at his age yet, but when he starts needing to organise his school books and take the right things to different classes it can cause stress and might need some support.
Some people (including Richard Branson, who is very positive about his dyslexia) suggest that creativity and 'out-of-the-box' thinking is often a strength of the dyslexic brain. That does seem true for us - although hard to know whether it's confirmation bias! Dyslexia is certainly completely independent of intelligence, and exists across the bell curve.
Dyslexia does bring very real challenges, but early diagnosis and intervention will really help. I can't emphasise enough that you shouldn't just 'wait and see'. It doesn't really matter what the cause is: whether the change of language has aggravated the difficulty, or whether that challenge is actually hiding an intrinsic difficulty. The same interventions and strategies will work, and hopefully also prevent the emotional harm which often comes from undiagnosed dyslexia.
There are some free dyslexia screeners, including one from Nessy (https://www.nessy.com/en-us/dyslexia-explained/testing-and-screening/free-dyslexia-pre-screener-ages-5-7) which might be worth trying. But I have known friends whose child passed the screener but were later diagnosed as dyslexic, so I wouldn't take it as gospel. (We didn't do the screener: it was a teacher who realised, but later than ideal)
Speak to your child's teacher. They've seen their written and spoken work (dyslexia is defined as difficulty with reading/writing which doesn't reflect underlying ability - which you would see in their spoken work) and also has lots of other children to compare with. But be aware that even experienced teachers can miss dyslexia, especially in a bright child who creates their own techniques to cope. Meeting expectations for reading comprehension absolutely doesn't rule out dyslexia. The difficulties may still be there - just worked around by your incredible child through enormous effort - and will manifest in various ways at different times!
The bar for the school to recommend an assessment on the NHS is very high. A private assessment is about £500, which you might consider. The assessor will want to speak to your child's teacher, so you should still be working with the school even if you pay yourself.
If not, the school should still put in place reading interventions regardless of diagnosis. But it does help to have the diagnosis. It gives you more leverage to ask for whatever it is they specifically need - like permission to use a kindle with dyslexic font instead of a book. Later, it will give them more time in tests, which will allow them to actually get their knowledge down. (imagine having to do all your exams - in all subjects - with 20% less time than the exam was designed for, and which everyone else does get. That's what an undiagnosed dyslexic is doing.)