I used to hate other kids being around Thomas, it would make me feel like I was some failure as a mother. It really didn't help that I have a cousin who is 11 months older than Thomas and who started talking when he was 10 months old! He could sing nursery rhymes at 13 months, could sign for also sorts of things and say complicated words like helicopter and butterfly perfectly. At family gatherings no one would even try to talk to Thomas because my cousin would be the only one to respond.
Thomas only chose to say so many words also. Daddy, teddy, car, one and bye were a few I can recall. He didn't say mummy until 2.5 or thereabouts.
There were lots of other kids that were similar in speech in our coffee group, funnily all boys. Sophie also has a friend who is 2 years 1 month and his speech is very much the same. A set of words he's used for a long time, noises and grunts in place of words, and some animal noises. Sophie has way more words than he does, but he communicates his needs just fine so doesn't bother with new words.
My brother also had difficulty with talking as a toddler, on a much worse scale though (like not till almost 4). He's the most talkative, successful one of the two of us these days. Has a whopper of an IQ too, around 160, mine is 118 and I was full on talking in sentences by 18 months apparently.
Thomas is perfectly normal with speech now and even shows quite a talent for comedic timing and comprehending difficult words and concepts.
Best of luck to Jack!