When you say you "went into the scanner", do you mean the whole body imaging/AIT scanner? As opposed to the walk-through metal detector?

If you actually went into the AIT scanner, I think I understand why they want you to remove your belt.

Both variations of AIT scanner, the millimeter wave (MMW) and backscatter x-ray (BSX) versions, work by passing their energy through your clothes, then bouncing the energy off your skin and back to the scanner. By measuring the energy as it returns to the scanner, the computer in the scanner can determine whether it bounced of skin, or bounced off something else. Anything other than a "normal" skin return is considered an anomoly, which must be investigated because it might be a nuke, or an underwear bomb, or a photon torpedo.

But the dang things are glitchy. They'll return "non-skin" signals from heavy folds of cloth, rolls of fat on obese people, ANY medical prosthetic (artificial limbs or breasts, colostomy bags, etc), and even return "non-skin" signals from sweat. That's right - if you get nervous, or it's really hot in the terminal, you might get a pat-down!

Belts, even canvas and cloth belts, are often thick enough to bounce the energy back instead of letting it pass through to the skin beneath. This results in a "non-skin" signal, which the scanner will flag as an anomoly to be resolved, and thus results in a targeted area pat-down of the area that returned the non-skin signal - in this case, your belt line.

Now, I've never experienced it, so I can only theorize, but my gut tells me that if your beltline shows an anomaly which must be resolved, you're going to wind up with TSO's hands going into the waistband of your pants. Yup, that's right - government agents will stick their hands down your pants.

So the answer is, NO, your cloth belt represents absolutely no true danger, but it does represent a potential false positive, and while I cannot excuse the TSO's shouting at you, I can understand why they'd want you to remove your belt.