We've all been through that kind of experience one day. The only thing wrong with your method is that you swapped equipment yourself, so you know when something was changed, therefore you tried to find something different.
If somebody else did the change and you didn't even know when something was changed, there is a good chance you'd never hear a signigicative difference, in one way or another. Or, rather, this difference would have been completely random.
It's not just you. All of us are subject to that kind of experience.
It's just that, as the brain can't hear everything, it chooses to focus on some details at will (and sometimes without us being aware of the choice). And that different focus leads us to think we hear something different. While we just look at a different detail of the picture.
I was chatting with some pro sound engineer a few weeks ago.
A typical experience we all had, during mixing a recording, is to decide to tune the balance of a track by adding bass or so. Then we hear the change.
Seconds or minutes later, we find that it's still lacking. We come back to the same track and change it again. To realize that either we were changing another track, or the EQ was bypassed. And still, we heard the change !
This happened to all of us.
