White was heading for a Grand Prix Attack (an early f4).
Going for this pawn formation.
2.f4 can be answered with 2....d5 so to save memory cells White plays
2.Nc3 first (also to disguise the Grand Prix Plan.)
The above pawn formation does no do any favours to the f1 Bishop
so White likes to play Bb5 (before of course d3) to chop it for the c6 Knight,
also White does not want that Knight landing on d4.
However.... (I hope you are taking notes)
They both play in and for the same club so Black knew White played
the Grand Prix Attack v The Sicilian so slipped in 2...a6 to stop Bb5
to cross him up.
In the game the c6 Knight did go to d4 and it ended up taking the Bishop.
I was speaking to Hugh today and he agreed taking on g5 was a baddie
but added right away that White played well.