English opening 2.g3 Nc6 3.Nc3 f5

In the book Grandmaster's repertoire: english Opening vol. 1 Mihail Marin says the following:

After 1.c4 e5 2.g3 Nc6, the accurate reply is 3.Nc3 as after 3.Bg2 f5 white lacks a useful move.

I dont understand this and I dont understand the difference between 3.Nc3 and 3.Bg2 in regards to 3...f5. Anyone understands this better than me?

If memory serves me correct, Marin recommends the 4.Nf3 lines, with the idea of 4..e4 5.Nh4, notice that the knight will not be trapped because the g2 square is vacant, often the knight will play Nh4-g2-f4, or something similar. If there is a bishop on g2 this type of line isn't possible.

That said, I believe Bg2 is absolutely fine, playing in a style similar to the mainline grand prix, but with an extra tempo. Objectively it's probably not as good as Marin's, but white wont be worse.

Marin is wrong.

The f5 lines are fun for both sides, white has just as good of a game going Ng5 in the nf3 lines with e3 instead of g3..