I'll try to explain:
Basically, Equestria Girls
isn't where all the ponies turned into humans (for the most part). What Equestria Girls did was introduce a mirror portal that connects the world of ponies to the world of humans. For every pony that exists in pony world, there exists a human duplicate. Literally a mirror world (aside from, y'know, being a completely different species and culture and whatnot).
The premise of Equestria Girls is that one specific pony (the purple one) had to go over to get her crown back from another pony who fled through the mirror (the red-and-yellow haired girl), and essentially purple pony has to remake friends with the human versions of her friends. The difference is going
through the mirror changes you from the natural form of one to the natural form of the other - or pony to human and vice versa.
To make a long story short, by the third film they've introduced the human version of the original pony, and at the end, human and pony-turned-human versions meet and thus prove they can co-exist simultaneously.
That is what Chris is playing at.
He loves himself so much he has other versions of himself (including the pony doubled up essentially) that exist just to kiss his ass.