@EdinburghCollective While it is not inconceivable that either player remembers all 31 games they have played on
Chess.com, it seems rather unlikely that GM Wesley So remembers each of his 1550 games against other grandmasters on the website. Note that in the first 11 games displayed by chessgames as being played between So and Mamedyarov, there are 11 different openings. Just because So had once played a Four Knights hardly means Mamedyarov would expect it in a bullet match, or plan to play it himself. In fact, in the same match he played a Four Knights type game beginning with 1.a3. I expect neither player prepared for this, but that the two games are unrelated.
Of course, I have no way of knowing this. You may very well be right that Mamedyarov was attempting to josh or goad So in that one game. I think two games are not necessarily related because they have the same opening, though. Take
www.chessgames.com/perl/chessgame?gid=1916241 and
www.chessgames.com/perl/chessgame?gid=1916241, which were played only months apart. Sure, there could have been hidden meaning, but I don't think opening choice matters so much to these guys. Most of them play every (good) opening under the sun anyway. At least that's my opinion.