I disagree. Telling the students there are three states of matter is just wrong and they have all the right to point it out. They keep that information for decades if not corrected/challenged and will give non true statements to others, their children, etc.

What the teacher instead should have said could may be: "There are many states of matter, currently we know of (amount). The most common however are these three: solid, liquid and gas. Maybe you will encounter a fourth: plasma. The others form in very specific situations that are very outside of our everyday life. You can look them up if you want to know more. But for this class, we only focus on the three most common."

Everything is correct, everything is clear. The scope has been set. Teacher still looks knowlegdeable and reliable. And most importantly: does not lie, tell false facts, he provides options for individual interests and builds trust and does not offer himself for attacks on his position by misusing the trust of the students by telling them factually false content.

Relying on groveling students is morally very bad as that's no relationship based on trust and respect for the pupils and can easily be challenged, like in this example. You would only be offering yourself for failure and risk your "dethroning", which is a bad foundation to build on from the beginning.

Depending on class structure another way could be to include the students and have the whole class collect the states of matter they know of. That way the "plasma" ones could shine and get heard. That way you will probably get to the common 4 but maaaybe someone heard of the BE condensat, which would be extremely cool and impressive. Wrap it up with "Great work everyone! Actually, we currently know of (amount) different states, insane, right? For this class we will focus ourselves on..." That gives bonus points for teamplay and class strengthening.