It’s not explicitly stated, but the obvious implication is that this was the only time Kirk met Pike.

Fortunately, there's just enough wiggle room to accept the alternate explanation that Kirk is saying "I've known him since his promotion to Fleet Captain".

The other slightly odd bit of mild discontinuity is that half of the main TOS characters in The Menagerie Part I (Kirk, Spock, Uhura, Scotty) know Captain Pike very very well, but none of them aside from Spock act like they do, nor do they display any dismay at discovering what's happened to their dear former captain (which Kirk only learns on visiting the base). Spock evidently has known for some time; long enough to have concocted his scheme and write the necessary route into a computer auto-navigation program, at least. But it's not clear whether anyone else found out before the episode. In any case, there isn't enough dialogue for these other characters in the episode to draw any concrete conclusions either way.