It's well known that he especially identified himself with the Minotaur, the mythical monster half-man, half bull: tender and bestial.
So, astrologically speaking, why would Picasso, a Scorpio, see a Taurus when he looked in the mirror?
Scorpio is the opposite sign to Taurus, of course, so the opposition itself is a kind of mirroring. But look the mirror itself is there, Neptune. Picasso was born with Neptune at 15° Taurus opposite the midpoint of his Sun and Mercury in Scorpio. For him bulls had all the glamour.