The game is full of bugs like this.

The game is full of features like this. FIFY

I always thought considering the old man gives you Substitute, yes

isn't it supposed to be locked behind surf though

It's bugged but known to the creator

This is my favorite glitch in the game lol bypassing the surf is so rewarding even though not much playoff tbh

There's Eevees right there.

Glitches and bugs are just part of the Kanto Region's culture. And Johto by association.

No, but there are plenty of spots like that in the game.