How is/was your day?

I think I have weak recollections of me once having made the same observation.  And weirdly enough, I think it was also at a bus station.
I'm going to offer you three hypothesis:

1: You may have discovered that most of us, by now, are alien reptiles in rubber masks.  The good thing is that we are now in full control, so you represent no threat and nothing bad is going to happen to you.

2: There is a difference between breathing through your nose and through your mouth.  The nose is built upon a crossflow principle that is not only widely employed in technology, but also highly visible in the biological world.  Have you ever wondered why Penguins' feet don't freeze?  Well same feature.  While human noses are not extreme adaptions to this, us being hairless Africans, it still has some effect in hydrating and warming the air as you breath in, and recovering both some of that heat and moisture as you breathe out.  You yourself has to be the judge of how this may have affected your experiment.

3: Maybe it's a question of that your own breath is easier to see for some reason?  I think I gravitated to that assumption all those years ago.  But it's hard to remember.

I have isolated my front window with draught strips tonight. It is already dark here, so tomorrow I'll look if I succeeded. So far, so good.