In American English, if something "bombs", that means it is very unsuccessful; it's usually used for stage acts, movies, that sort of thing. If a joke bombs, it's so bad that nobody laughs.
A real bomb might have a fuse. Although modern bombs now have a detonator that might be set off with, for example, an electric charge, an old-style bomb might have had a fuse, a short piece of string or paper which has to be lit, and then burns, giving you time to get clear of the bomb before it explodes -- like you might see in a Warner Bros cartoon.
The critic is saying that the comedian's jokes are so bad, even the Army thought he was a real bomb.
(The critic doesn't really believe people could mistake people for real bombs, but he or she is using hyperbole -- exaggerating the idea to make it seem ridiculous.)
Student or Learner