I generally agree with you that it was most likely a bumbling mistake as opposed to something devious that the detective was doing. But, you have to admit, he couldn't have made it look more suspicious had he tried.
I didn't see the detective's testimony, but from what I read on here, he was otherwise very thorough and took meticulous notes of everything that was done, every interview he did, everything he found and where. But then when it came to the phone, he waited a week after talking to the AT&T rep and then just winged it from memory? And then when he got a warning that it was about to erase everything on the device, rather than stepping back and thinking "maybe I should get some help with this before I screw up", he just went ahead and erase it.
I also think it is at least a tiny bit hypocritical for those who are sure that Brad is guilty to be saying "Oh, it's unimporant. There wasn't anything on the phone, etc." What if Brad had done this? What if his story was, "well, I just went from memory" and "when it told me it was going to erase everything on the device, I didn't realize it really meant that". Everyone here would be saying that's absurd and just another of Brad's many lies, there is no way he didn't know that he was erasing everything.
So again, I think it was probably just a poor decision followed by a dumb mistake, but they handed the defense something to make a big stink of. You can't blame the defense for using it.