The Welsh outfit sprung a major surprise on Saturday by spoiling the Dutch coach's Premier League debut by triumphing 2-1 at Old Trafford
The Swans triumphed 2-1 at Old Trafford on Saturday in Van Gaal's first competitive game in charge since replacing David Moyes at the helm this summer.
And Van Zweden says while he has a lot of respect for his fellow Dutchman, he took great enjoyment out of Swansea spoiling his compatriot's Premier League debut.
"I had a great day! United thought they signed a giant with Van Gaal, but we really showed them on Saturday," he told NOS. "I saw scarfs and banners with his face all over town."
"We played a really good match and deserved the three points. I have a lot of respect for Van Gaal, but we put him with both feet on the ground.
"I mean, if you have a mediocre squad like United, it's going to be tough. I really hope for Van Gaal that they sign some players, because with this team they will end in the middle of the table."
The Red Devils have been linked with a host of players this summer and hope to conclude deals for Sporting defender Marcos Rojo, Ajax's Daley Blind and Fiorentina winger Juan Cuadrado before the close of the transfer window.