There's a possibility its been nicked
Yep - the thought has certainly crossed my mind. I can't imagine the original owner deciding it had no value.
However it was pretty filthy (dusty) when I got it. the wheels in particular were covered with cobwebs. This makes me think it's just been sitting in a shed for a while, before being binned in good faith by a relative or someone having a clearout. I'm fairly comfortable with it at the moment, although as you suggest I'll make gentle enquiries at LBSs & local groups before counting any chickens.
That will be a garage/shed 'I've given up cycling, I'll take it down the tip to see if anyone wants to make use of it' type find. Looks to be a legit 'tip find' of the highest quality.
I get it all the time when its been sat and the wife wants room or people are moving house.