So, yes, some of it may be the way you perceive the piano after not playing it for a week, you may even be hearing things you hadn't noticed before. Since you mention sustain, if it is an upright, you may be noticing the after ring that is common to all uprights but is rarely noticed. That would be a credit to your increasing sensitivity.
Apart from all this, the piano can change from not being played.
I would agree that the picture is usually multi-dimensional, since the whole piano as a machine, mind as somewhat unknowable, and interaction of the two are so complex.
Acknowledging that, it still is often the case that as I teach my clients how to listen again to the sounds their piano is making, instead of pretending entirely to hear the sound they want to hear, they become more acutely sensitized to what is happening, and less willing to accept the sound going too far south.
Increased sensitivity can quite possibly have an excellent effect on your playing and/or your experience of your music. With my own playing, it took me way over a plateau I had been stuck on for years. It may not be like that for everyone, but it sure was for me.