Yes, and that is part of the problem. Like some ancient Greek philosophers, some Buddhist thinkers (and nonthinkers) dismiss creations of the mind (thoughts) because they seem transitory and changing. It is the ancient prejudice that only things that are unchanging and permanent are real. But as I have said to others in this comments section, that thoughts are fleeting does not make them unreal. No, not all schools of Buddhist thought make the mistake of declaring all thoughts are illusions, but some do and I was responding to that. As for Nirvana, that is the release from the cycle of death and rebirth. It is the state of nonbeing beings in being, one is within saṃsāra. As I said to someone earlier today, Buddhism is based on negation — the desire to negate the self, negate being. That desire blinds it to certain realities, which one could say is its intent. That is why it makes the mistakes it does about thoughts and self.