One thing I can think of is that after 2. Nc3 you still have a chance to transpose to main lines after 2 ... d5 3. d4, so it's a tad more flexible. I know it's a stretch, but if your opponent is (for whatever reason) afraid of the two knights variation, they might not play 2. .. d5 and opt for 2. ... g6 or other inferior move.
Don't try this at home. ;-)
First of all, a simple LiChess search gives this is B12 Caro-Kann Defense: Advance Variation, Tal Variation, i.e. it has even a name and is legit.
Second, 8 games listed, with IMs playing it, so it's still rare.
Third, standard Black move is Kb8. He doesn't even try to immediately throw everything except the kitchen sink at the ...