Netherlands captain Van Persie was publicly criticised by manager Van Gaal in the build-up to Saturday's 3-0 win for his "very bad" performance against former club Arsenal last week.
But Van Persie responded by lashing home United's third against Hull, after teeing up captain Wayne Rooney for the second.
Van Persie's goal was his first for United since the 1-1 draw with Chelsea last month, however, Van Gaal still believes the forward can improve on his showing at Old Trafford.
"Every striker needs a goal, when you don't score in the last two or three matches, you need a goal," Van Gaal said.
"I'm very pleased and happy for him but I'm sure that he can play better than today [Saturday]."
Van Gaal was delighted with United's overall display, which he stated marked the first time that they have controlled a game for the full 90 minutes in his tenure.
"This is the first match that we have dominated from the first minute to the last minute," he added.
"We knew already in advance that they [Hull] come probably with five defenders and a full midfield. We have trained to play the ball quick and we did it.
"We have great moments in the game, creative moments, also the preparations of the goals and the chances.
"I was very pleased with the performance and the result."
