By itself? It'd be a stretch. When found with a bullet, Osama Bin Laden merchandise, a journal detailing how you can revoke your US citizenship, and trips to Pakistan and Afghanistan...
Of course, if the bullet was really just the bullet without the propellant (that was not clear to me) then yeah, I agree with you.
[1] I think It's the explosive powder that matters here. A bullet with no propellant is just a lump of lead, which I think would be okay.
From your last sentence, I can see you are no stranger to making snap judgements without all the details. ;)
The article itself says that the customs agent "suggested that I had used the burqa in order to move undetected throughout the tribal regions of Pakistan and Afghanistan". Seeing as he is not a Muslim and wouldn't have one for religious reasons, that does seem like it might be a fair question.
I travel all the time, and our security system does not protect anything but our peace of mind.