Yes, it wasn't hard to get that many people for a tourney. I went to New York City to play in one that had over 300 people. And multiple ones in Detroit with over 150.
And its wasn't hard to make money at it when you had really no bills. Food, Gas and fun.

Me and a friend would travel from town to town and play at game stores. Back then we'd play the way it was meant to be... for ante. So I'd win a bunch of cards, trade those back for more cards... sell some... etc... throw in conventions where I'd make more $$$ selling and trading cards and it was a blast.
No money directly from playing in tourneys but enough from selling cards. Figure at one time or another I'd have at least 3 black lotus, and a couple dozen moxes... it wasn't hard.

Ah yes, if you were selling the cards, that's definitely believable. I didn't even think about the playing ante, that's way before my time. Losing a Mox or Lotus would suck.