This one might need a bit of explaining because I myself got confused when translating it.

The guy sucks at fingering, and the girl tells him as much.
He then starts using more force instead of changing up the technique. (he's the "hardworking simpleton" type)
She tells him to change up the technique instead, "like how you would stroke someone's head".
But he misunderstands that and instead starts stroking her head while continuing to finger her vigorously.
Turns out she actually likes this new arrangement, and now wants him to go harder.

So that's why she's telling him he sucks so much while she's obviously squirting, its because she wants him to go harder.