Even for those without Pre-Check, it's not odd to leave tablets, iPads, Kindles, etc. in the bag. The (non-precheck) TSA standard is to let you leave smaller electronic in the bag. You only need to remove large electronics (laptops, full-size video game consoles.

https://www.tsa.gov/traveler-informa...gh-line-faster

As with the others, I've experienced it in smaller stations where they weren't operating separate pre-check lines, or they were sharing x-ray machines. My bags got the standard screening (laptop out), but I got the pre-check metal detector.

If, as the OP mentioned, this was a dedicated line perhaps there was something he couldn't see that necessitated regular bag screening (staff training, security concerns, etc...)