I have no idea whether or not Tesla's stock is over-priced. However, it is definitely more than an auto company. It has a solar division, and it make electricity storage systems for home and utilities. Also, there are strong indications it is about to go into manufacturing li-ion cells. It seems to me it is quite possible that at some point it will be worth a trillion.
Let me add it is interesting that people who say Tesla is over-valued so often make this mistake, even though most of what I said is widely known. Perhaps people are being intentionally misleading.