Well, one of the things about food sites is the question of identity, branding if you will, surely, the first thing they teach you in Marketing 101, differentiation.
So, Chowhound.com was the first to throw off the divisions. There were (chowh)hounds and there were foodies. Of course if you were on Chowhound.com, you were a hound and cool. And the rest of the world was foodies, well the rest of the food obsessed food world was a foodie. You can actually read Chowhound's worldview on the subject here:
http://www.chowhound.com/misc/faq.html
Now, I agree with Chowhound, that there are people who are as much into the scene of eating as they are into the food. That the chef's can be more important than the food, but I am not quite sure that Chowhound's definations, as linked, do that notion right. To me then, the terms Chowhound and foodie are roughly interchangable.
Chowist. Well, it was thought when people would not so much be hanging on a site called Chowhound, that perhaps there would be a better term to describe the denizens of such site. Chowist was one such word thrown out, but it is not necessarily one of huge use. It's not so much that I dislike the word per se, it's that I DO like the word Chowhound. Maybe it is sentiment, but I like the implication of hounding of sniffing out good food, and I like the implication of being in a pack, a pack of like minded folk.
That's how I look at the words.
Rob