There may or may not be a connection. Given Tiamat's Scan data--

Used to be a GF. Became a monster under Ultimecia's power. Its Dark Flare destroys all enemies.
--many people have speculated that Tiamat is a corrupted version of Bahamut. Whether or not Squall obtains Bahamut is actually inconsequential, since the "rules" of Time Compression are debatable, and it's therefore impossible to suggest what "events" are impossible. However, while the supposition can't really be proven false, there's also no way to prove its veracity.

There are other possible theories, of course. One could suggest that it was Selphie's mysterious GF--

Selphie: When I was 12, I went on an outdoor training session. I found
a GF inside one of the monsters I defeated... I junctioned that GF for a
while. So I have experienced with GF, too. But...but, it's really weird!
I can't remember the name of that GF!
--or make any number of similar suggestions. Based on the game alone, one unfortunately can't come to any definite conclusions.