For sure, anything is possible.
The distance honestly doesn't make much difference to me, whether he's 3 blocks or 3/4 of a mile away. I cannot emphasize enough how close to impossible it would be for a local to accidentally end up in the river in that area, regardless of how far away from it they started.
To get to the edge of the river, one would have to cross through a park that's like 100 yards wide and somehow not notice it at all. Everybody there knows the river is immediately beyond the park. You'd have to be out of your mind to a level that I can't even fathom, and I can fathom a pretty high level. There's also a heavy metal chest-high fence at the end of the park blocking off the river that a 5'9" man would not go over if he ran into it, even if he ran into it at a full sprint.
That being said, the fact that he disappeared period from the area that he did and hasn't been found in a week and a half is similarly unbelievable. And the possibility also exists that if he backtracked toward the river he then tried to cross one of the bridges, which, while still extremely unlikely, is about 10,000x more likely to result in ending up in the river than the accidental park scenario.
Every option in this case seems so improbable that I think there's a decent chance that he IS in the river, but almost that entire chance consists of the bridge scenario, suicide, and the possibility that someone put him there.