Solskjaer has won 14 of the 19 games since he took over as interim United boss in December, but Van Gaal insists suggestions the Norwegian has transformed the club amount to 'fake news', the kind which he says has been present in football for half a century.
"People think we have only had fake news since Donald Trump became president. In football we have had it for 50 years," Van Gaal told BBC Sport this week.
Earlier in the same interview, the Dutch coach had attacked claims that his style of play at United was boring, putting it down to the way opposition teams were playing and a lack of the correct personnel to make his 'philosophy' work as it required a higher tempo.
In his eyes, United stopped attacking when Mourinho was appointed and little changed under Solskjaer, while the team is no closer to returning to Sir Alex Ferguson's style.
"[Mourinho] changed to park-the-bus tactics and played on the counter. Now there is another coach who parks the bus and plays on the counter. The main difference between Mourinho and Solskjaer is that Solskjaer is winning," Van Gaal explained.
"I am not there but there does look to be a change and the atmosphere seems to be better. It is also true that Solskjaer has changed Paul Pogba's position and put him into an area where he is much more important," he added.
"But the way Manchester United are playing now is not the way Ferguson played. It is defensive, counter-attacking football. If you like it, you like it. If you think it is more exciting than my boring attacking, OK. But it is not my truth."
Speculation has emerged this week that United no longer see signing a new centre-back as a priority this summer after the way the previously porous defence has improved under Solskjaer.