I suspect what happened is that the officers felt that the pair of pliers was a "concealment" because they were hidden inside the lining of your bag (which is why you didn't notice them and remove them before your trip). It was an innocent mistake on your part. But to the officers, it might have looked like you were trying to sneak the pliers through the checkpoint without proper inspection.

It doesn't really matter what you said about the repair shop (just a story, after all); what matters to them is what the evidence shows....and frankly, if it weren't what you said it was, it would seem a lot like a concealment.

Potential concealment = less likely for TSA to want to trust you.

You could apply for Redress, but that process is more for pax who continually get SSSS.