iPhone 5 has returned from repair with loose screw - stripped?

My girlfriend's iphone 5 just came back from repair and the bottom screw (next to the Lightning connector) dropped out as it was loose. I dropped the screw back in and it fell nearly all the way, sticking out only half a mm or so maximum. I moved it a quarter turn with my finger and now it grips, but i don't anticipate it staying there long without being torqued up correctly.

Thing is, I'm surprised how much the screw went in without tightening (and it would drop out just as easily). Is this normal on the iPhone? We don't know whether to send it back because the thread is gone or get the necessary tool to screw it back in? I'm not keen on loosing the screw at some later date if it can be avoided.

Any advice much appreciated!