Do swans understand the concept of "Hello" & "Goodbye"?

Hi! I read online that swans greet each other with a nod of the head.  So when I approached a couple of swans a few months ago I'd nod my head and after a while they began reciprocating.

When I leave them I always say "Bye" or "Going now" as a signal that feeding time is over and after a while I noticed they were doing the head-nod greeting to me as I left.

This may sound like I have an overactive imagination, so here's the video evidence :)