As soon as any crypto currency will not have demand and the price will fall in a matter of hours - this can be called a bubble in the cryptomir. And such a moment can happen even with bitcoin.
As long as they have the demand that is sustainable and there is a real life usage for it, then we cannot classify such an asset as a bubble. Yeah, nothing is predictable, but there are some times we just need to use our head even when investing as there would always be some strange movement in the market that should make any investor scared, but all the same, we have a future in our hands and that is all that matters.