I think they had the model already from Meet the Spy
I'm just on the assumption that if Valve uses a character in their videos, it's gonna be more detailed than what's seen in game or whatever, like they've done with the CS:GO characters and the family from the last page of TF2's Smissmass comic, so it seemed like a valid thought at the time that Valve would use someone else's model rather than their own
But thinking back on it, i feel like a dumb dumb