Depends on your definition of "bubble".

Here's financial asset X. There are changes in the fundamentals. X becomes a more attractive asset. People notice, and buy, and so the price goes up. That's not a bubble.

People see the price of X going up, and decide that it's a good investment because the price is going up, so more people buy, so the price goes up more. That's starting to become a bubble.

2008 was definitely a bubble. People were buying because the price was going up, not because of fundamentals. A lot of people got burned when the bubble popped.

This? I'm not so sure. If there's an imbalance between supply and demand, is that because of fundamentals (not enough houses)? Or because people are buying because the price is going up?