The MLB.com report also literally states that Murray 'needs to improve to play there in the big leagues', I don't think I'm being uncharitable when I assume that a good team is not going to want to play Murray at 3B at the MLB level with frequency. As with most things with prospects that could change good or bad with more info/dev time, but to answer your original question, that's the basis for thinking of him as a positionless bat.
Otherwise, that's a real wide range of prospects, ranging from a 1st round pick shredding A+ with positional value to guys hitting as well as Murray a level above, to unrefined projection plays, to guys who I think of as similar(McGeary) or worse(Perlaza) prospects than Murray. I had Murray in my most recent Top 20, and if you're convinced he's a functional 3B then I would get the instinct to rank him even higher, though I don't really see the case for Top 10 if we're including pitchers.