probably as you suspect a combination of all 1-4 , I know someone , wanted to live on a particular street and put a note through every door offered them £25K over asking price for all the properties on the road, that was in the late 80's during a slump in house prices, BUT they wanted to live on that street and particularly on one side of the road, and they did get one of the houses and are still there , it is a vey nice property to be fair - House was about £100-£120K market price (in middle 80's) , nice 4 bed detached , in a sought after area
I have had that in the past, I just assumed it was some commercial company pretending to be a private buyer.