@Steve ******
“He could also apply to extend it by 1 year if he meets the criteria”
If you mean the visa by using the word “it”, you are technically in the wrong
I am going to say it AGAIN and you should READ carefully, so you maybe understand the true meaning.
He cannot extend a "90 days single entry Non-Imm-O visa" by 1 year
You cannot extend a visa at all.
He can only apply for the "one year extension of the stay permit" - based on being married to a Thai wife.
You cannot extend a “visa”, and you cannot extend a single entry 90 day visa, because a single entry visa becomes invalid by the moment he enters Thailand
He can only extend the 90-days stay permit he has been stamped in, by fulfilling the criteria. This is the only point where you are correct