I haven't caught a wild Charizard before, but I touched a Charizard at a gym. When I check my Pokédex, Charizard's shadow appears, and it says I've seen 1 and caught 0. I don't think I seen a wild one before and it isn't in my journal list either... so does that mean I'll see a wild Charizard soon?
No. This was actually just added in the recent patch.
Trainers, did you know that Pokémon can now be discovered by viewing Gyms? New Pokémon are logged in your Pokédex!
— Official Twitter post
Now, when you click on a gym which contains Pokémon you haven't seen before, they'll be added to your Pokédex and update the Seen tally.
This has no effect on your chances of seeing that Pokémon.