iphone 6 issue - sudden battery drain

First off my battery is at 100% health.

Second, I did something stupid yesterday, but need to get some idea from those in the know.

Story:
I was going to an Apple Store yesterday to get my cracked screen replaced ($129). Walking through the mall I passed a cell phone repair place. I asked the kid working there how much they chared. He said $60 and would take about 15 minutes, so I said go ahead. I also asked him if he could put the phone into the new Otterbox defender case I bought online.

Here's where I was dumb. I was distracted thinking about other stuff, and it wasn't until out was out of the store and maybe 5 minutes down to the other end of the mall when I realized I had left my phone on. Didn't even think at the moment to turn it off.

I went back, the phone was done. Paid and left.

At 7pm, I went to the pool, and glanced at my phone before getting out of car, and saw the battery was a 40%. Got back in the car at 8pm, looked at phone, and battery was at 21%.
I was alarmed, as obviously it still should have been at 40%

My battery is at 100% health. I just had a new one installed maybe 4 months ago.

I went home, plugged in and spent the evening going through each and every setting, every app, etc. I have.
I cleaned my cache,
Deleted apps I don't use often/ever
Turned bluetooth off.
Deactivated a bunch of other stuff.

Looking at my battery usage, yesterday I see the usual surge around noon when I use my lunch delivery app (I deliver group lunches) mostly normal usage between about 1pm and about 8:30. It was actually very low usage at the time I was at the pool. Then a spike from 8:30 to about 9:30 while I was working on the phone. Then a final spike from midnight to about 1am, when I went to bed.

I left the phone charging all night. Woke up at 7:30 with it charged to 100%
Unplugged it and snoozed. Got up at 9am and the phone was at 87%, while I slept. It's 9:23 now and it's at 84%.

Normally if I go to bed with the phone at 100%, not plugged in, it's at 100% or like 99% in the morning.

I'll have to keep it plugged into my car from 11am to 1pm while I work, then I'm going back to that store and ask what he did.

Honestly? I don't use a passcode to get into my phone, as I keep no financial info on it, and it's always on me when I'm out.
However, I noticed right away that when I hit my home button to ativate the screen, I got a message I had never gotten before, something like "Unable to activate passcode.

I have a 2 o'clock hair appt, but I'll go by to talk to the kid first. After the haircut I'll go back to the Apple Store to talk to them.

Anyone have ideas?

What could he have added to the phone that I can't see that is draining power?