I strongly suspect your last suspicion is the correct one.

Somebody got fooled by it and subsequently donated it.
These have been for sale in TKMaxx for a good number of years and do frequently turn up on "antique" stands in fairs, boot sales etc.
Some are good enough to fool - but that's just the luck of the draw.
The Oxfam I give stuff to always says I hand in great stuff too.

It's all just stuff I've decided is second rate and don't want any more. But if it was good enough for me to have bought in the first place, it will sell again.
They did get a good few bits I'd got in TKMaxx and just enjoyed for a short while, until I needed the space.