Definitely not funny. At least he now knows something he did not know.
I would give him the benefit of the doubt and, as you did, just explain it to him.
As a rider, you have to be riding on the defensive. The lane was free but you have to expect these things and be on the lookout ready to react. This way, not many things will catch you with the guard down.
You were alert and reacted and nothing happened. Then you noticed that the cager was playing with you (signs of ignorance). There are way too many more ignorant cagers out there than there are smart riders.
Ride safe, ride smart and be on the lookout.
Glad nothing happened and that both of you still have your theet