no, what the nazis said is that it was the communist party, not a lone communist:
Despite the fact that Marinus van der Lubbe claimed to have acted alone in the Reichstag fire, Hitler, after having obtained his emergency powers, announced that it was the start of a wider communist effort to take over Germany. Nazi Party newspapers then published this fabricated story.[19]
If celebrating keeps morale high I don’t see much harm in it. Sure, in a just world he would have gotten a trial, and sure, it won’t change anything, but you gotta take what you can get.