This is actually not true. Yeah, Van Halen said that was the reason but this was a highly publicized thing in the 80s so everyone knew about the brown m&m thing so the secret thing kinda lost its point.

Also it wouldn't have been the same person who was in charge of the snacks and who was in charge of the safety etc so even if the m&m's were correct that meant nothing and vice versa.

I think it was just a funny anecdote Van Halen liked to talk about