What is going on in this situation regarding inter-floor noise?

I've been hearing some thumping sounds from the floor above lately.
After enduring it for a while, I went upstairs just now to say something. I rang the doorbell
and told them that I hear the noise periodically.
They said via the intercom that they would be careful, so I came back down.
But 10 minutes later, that person came down to my place instead,
saying that while they admit to the noise just now, they don't know what I mean by "periodic."
They said they felt I was misunderstanding them and that they felt they had to come down
to make it clear that it wasn't the case.
They said, "I admit I was walking around a bit just now, but I think you're misunderstanding the part about hearing it periodically."
So I told them I would observe a bit more and speak to them again, and that I might have been a bit sensitive.
What was that person thinking, saying they would be careful and then coming down 10 minutes later to say that?