There is a very big difference between giving no credit and giving a fair amount of credit, which might be small. If you listened to the podcast they talked about Aaron in a non-disparaging way, and a way that I'm sure is accurate to their beliefs about it.
But my point is that _even if_ Aaron was super, super important to the company 16 years ago (which I can't speak to), Reddit was a tiny little fledgling of what it is now. From what little I know about Reddit's history, I know that Aaron stopped working on Reddit very soon after he started and has had no contribution to the company since then.
I also do think it's interesting that the people that have worked at Reddit for years/decades all seem to have a similar opinion of the situation, and the people who haven't worked at Reddit at all are the ones that feel so strongly that Aaron is being wronged somehow.
Maybe Aaron himself was more proud of all the other things he accomplished! Saying he was an important but small part of Reddit's story is still something!