Not unknowingly he did in the Star City 2046 episode back in Season 1. Wally West probably told him in Season 3 with Earth 2 Wells.
I don’t Know
Seems he knows about the multiverse now, and by what Sara said in Crisis, they figured it out offscreen back in Season 1.
There’s a 5 year gap between him leaving the team in s2 and meeting the team again in 3x01
What do you think?