This seems more like a case of different news outlets cobbling things together. It all stems from an interview Gakpo had with the NOS.
He basically said that Utd showed interest weeks before the deadline, but that interest started to wane as time moved forward. Then towards the deadline, and especially in the final days, there was concrete interest from clubs Southampton and Leeds. His decision to ultimately stay at PSV was influenced by a combination of factors that he weighed, including a conversation with Van Gaal in that regard.
Which makes complete sense. Talented as Gakpo is, he’s far from a guaranteed starter. Even in the national team. And imo Gakpo’s chances of playing in the World Cup would have been hurt had he moved to either Utd, where he would have no guarantees of starting, or Southampton/Leeds where he could struggle at a mid table team.
At no point, in any of the interpretations from media outlets, did I read animosity towards Utd in this particular instance from Van Gaal. Just Gakpo making an informed decision based on several factors.