Serpentine belt tensioner was locked while mechanics were working on the car and they couldn’t complete the work until it was replaced?

2006 Hyundai Tucson - I took my car to the mechanic and they found an issue with the power steering (which was the reason I took it in to be checked) and the rack and pinion. They took things out to fix them but, according to them, as they were putting things back, they noticed that the serpentine belt tensioner was in a locked position, and they couldn’t finish the job without replacing it. They charged me $124, “just a few dollars above what they paid for the part and no labor because they couldn’t finish the job without that being fixed.”

Does that sound legit? I really hate being so ignorant about cars so I could really use some direction.

Edited to add: V6 engine, if that makes a difference