Good points, @sorin.cristescu.
A market bubble is really just a synonymous term for "buying craze", after all. Excitement tends to attract more excitement (from other people), whether we consider fans in a stand at some sporting arena or children singing "happy birthday" around a cake or participants of the (stock) market or ________ (name any "event" where people come together to share in some type of activity). Like you said, on the market side this translates into a self-feeding loop of positive expectations that attracts the next buying wave(s) and quickly snowballs into the parabolic moves that are the hallmark of bubbles.