Does not necessarily mean that he was moser.
+1
And even if he did rat on them, it doesn't automatically mean he's halachically considered a מוסר. I just heard a shiur that touched on this topic, and there's all sorts of shitos regarding what is and isn't considered אונס, where one wouldn't have a דין מוסר. Obviously someone in this position should ask a major posek what to do, someone with big shoulders. I have no idea if this person did that or not, but we shouldn't jump to assume that he's a מוסר.