During your training you were given a value of having to do mask clears. While it may be common for another diver to kick your mask causing it to flood or even making it come off completely. There are other reasons of a more natural flavor. While this may not happen on every dive there is always the possibility. Please note that in both videos the seal is just playing – it is NOT attacking the diver! In fact the seal was very gentle.
I know Janine has played ‘monkey see monkey do’ with the seals in California but has never had one want to wear the mask.