Icardi scored Inter's second and third goals in their 3-0 win at San Siro on Sunday, their first win in four seeing them rise to ninth in the Serie A table.
Mancini said Icardi's lack of exuberance after each goal was down to a strenuous relationship with the club's fans, as the Argentinean striker and Fredy Guarin saw their shirts thrown back at them in Sassuolo after handing their tops to supporters.
"In my opinion you should celebrate after a goal," the former Manchester City boss told Sky Sport Italia.
"I don't think he's unhappy, I assume it's a leftover from last Sunday. The fans cheered him, so it seems to be sorted out.
"Guarin played well, though at times he gets a bit stubborn with the ball and can lose his way.
"He's perfect as the deeper point of a midfield three, as he plays the ball well and has great power."
Mancini said Inter's performance on Sunday differed little from their losses to Napoli and Sassuolo, the Italian claiming fortune was not in their favour previously.
"Tonight's Inter is the one I wanted," Mancini added.
"It's also the one I saw against Napoli and Sassuolo.
"The only time it wasn't my Inter was against Empoli, as in the other occasions we made costly mistakes.
"We have to keep training, as things are starting to go our way and at times you need a bit of luck too."
The luck that went Inter's way on Sunday was in the form of Palermo's profligacy, as Franco Vazquez hit the woodwork with the visitors trailing 1-0 early in the second half - while Luca Rigoni also missed a gilt-edged chance in the first stanza.
"I don't know how Dodo made that mistake, as he had a team-mate three metres away and wasn't even under pressure," Mancini said, of Inter's defending when Vazquez narrowly failed to equalise.
"This is the kind of error that we paid for in the other games. We cannot keep giving the ball away in these situations."
