At best 2.Bc4? is a loss of tempo, at worst it shows no understanding of opening principles & as you suggest is a common response in the Sicilian.
It seems to be popular with -1500 players.
My initial idea was:
then the forced
& black has a big lead in development & a great position
white to move
but I have come to thinking 2...Nf6 is too freeing for white, for instance they can play a simple 3.d3 or maverick 3.e5!? as hereGame 3156832
Now I believe the straightforward 2...e6 then 3...Nf6 & 4...d5
is best & can be played against virtually anything white throws at you.
With anything like accurate play from black 2.Bc4? in the Sicilian gives black either a lead in development or a free hand in the center or sometimes both!
On gamesexplorer black wins around 60% after 1.e4...c5 2.Bc4?
I think that accurately reflects the value of the move!