No, not probably, Hopper admits that the weed being smoked throughout the movie was "real" not just a prop, in fact he stated that the cost of their weed was factored into the budget for the movie.
Don't be to quick to discredit people's statements just because they are stoned, especially when they're on chemicals that awake our consciousness. If they were drunk I'd question their perception but hallucinogens enhance perception especially in such matters as UFOs, after all consciousness is the driving force behind their ships' propulsion and navigation systems.