Grabban, a former Millwall player, scored Bournemouth's fourth goal from the spot, but amidst the celebrations, fellow Cherries player Cook was left with a gashed head after a coin was thrown onto the pitch.
"I can understand his celebration," Howe told the Bournemouth Echo. "Crowds can shout all they want and abuse players on the pitch.
"What are the players supposed to do? Just take it? I don't think he's done anything wrong or untoward."
The result sees Bournemouth climb to eighth place in the Championship table.