I actually listened to the testimony and Bradley says that Hernandez told him something along the lines of the following:

"[that a special ops guy had told the team Iphones could be used to record you even when they are off.]"

This sounds similar to what others have claimed about the capabilities of certain government agencies. Also, given what many believe or has been shared in the media (also in Data and Goliath) I think it's hard to make the claim he was paranoid as a result of not wanting iPhones around.