Good result. "Replace everything" usually works, and is what shops like to do on your dollar. Had you placed the blk lead right on the BATT neg post, you might have found your battery was holding 12.6 V and the drop was thru the connections. I hope the parts store tested your battery before selling a new one.
Funniest "won't crank" issue I had was helping a friend at night in an apartment parking lot. We were both new employees in temp housing, so had few tools at hand. He couldn't get anything from his new battery. Finally, he got a flashlight, looked close and found he had left the black plastic cap over the neg terminal. Cranked fine after that.