When you’re trying to draw something at least a bit symmetry you want to flip the canvas horizontally to see if it looks good the other way around as well.
The reason artists do that is to ensure their eye hasn’t “grow accustomed” to seeing the drawing always from the same perspective, preventinng them from seeing any mistakes they might have done.
I do this even with traditional art if I’m using low density paper (is that how you say in English?). I’ll turn it around (so that I’m looking at the back of the page) and hold it against the light.
Kekeflip jokes by making the flipped drawing horendous, to emulate the feeling artists get when the drawing is flipped and they realize the eyes are not symmetrical, the mouth is crooked, etc etc…