Oh, please. Tell me, when you have a device plopped in front of, and you're asked "hey is this a bomb" that you'll be able to think rationally and dismantle it, and of course, recognise what it does.
Well first off if it's only a few inches long, and 90% of the insides are empty, the only area where they could possibly have been explosives is in the display, that was the largest part. However the fact that the display was functional at all indicates that it wasn't filled with explosives, otherwise, obviously it wouldn't work. Using that you can conclude that even in the worst case scenario there's less than a cubic centimeter of explosives in it. Would someone even bother with less than a cubic centimeter of explosives? That could take out maybe 1 person at point blank range, tops.
Really now, that required like a few seconds of spacial observations.