I saw this posted in the heavies but it was a different video. I almost never check the heavies but it was linked on the homepage so I had a look and commented. Sergey is a fan of Conor, or at least is pretending to be, and wished him luck heading into his fight with Alvarez on Twitter (probably for Khabib to fight him for the title & make a lot more money). Sergey's been wanting to see Conor fight Khabib, his friend, for a while now so it may have something to do with him getting the next title shot. The chest poking is something I can't explain, and if you look at Conor's facial expression and his eyebrows, Sergey said something he apparently didn't like early on. Hmmm.
Here's another video from Fancy Combat that was posted to YouTube. I'm not too good at reading lips but I wish that we had the audio of the whole convo.