Moon storm - reception expectations are extremely low if you have a child who already reads, and understands number bonds etc. That said, they are extremely high if you have a child who can't recognize his or her own name written on their peg.
4 and 5yos vary so much in their development.
Nevertheless, a good school should be able to cater for all yr r children, whatever their individual needs - so if a child enters already reading fluently, they will be allowed to access books from other year group shelves instead of the reading scheme (or started on the scheme wherever appropriate).
The first few weeks of yr r are really all about learning the new routines of school, and the teachers assessing the children individually to gauge what stage they are at. Most of the learning at this point is through play , but there are lots of opportunities within this for children who have already met the learning outcomes of yr r (and 1/2 whatever) to extend and practice their skills. Eg just the role play corner and the shop - lots of maths and writing for those who love to play with that stuff, and interaction for everyone.
There will always be a reasonable percentage of children who can ace the yr r (and indeed 1/2) stuff on entry, just because of the laws of averages. All kids are different.
If ds is happy, I would let it go, and let him get used to the environment. You can discuss the academic stuff at the parent's evening in the next month or so, as the teacher will share where she thinks he is working, and what he will be working on or towards over the year. If this is stuff he already knows, then do mention it. Some children do get overlooked.
A teacher's job is to help all children meet their own potential, not to turn out identikit models that only meet early year's expectations.
A lot of it is learning where your child sits in relation to his peers. All of our 'norms' get modified a bit on school entry as we see a wider range of abilities on display instead of those we are used to at home.