iPhone reports 2 Hotspot connections even though only one of my devices is connected I connected to an iPhone Hotspot with a MacBook. I got internet access. Within 15-sec, the iPhone said there was a second Hotspot connection. I toggled Hotspot, reconnected, and still 2 connections. Finally, I turned off Hotspot, changed password, and re-connected the MacBook. A second connection did not happen.

My initial password was not easy to guess p:Fucrj346Q!. I've never been in this location before. What could have caused the iPhone to report having 2 connections initially?

note: I'm at a hospital where there is an enormous number of magnetic / electrical / radioactive based monitoring equipment.
Other devices (including iPads, iPods, Macs, and other iPhones) connected to the same iCloud account as your iPhone will, if in WiFi range, automatically connect to your iPhone's hotspot when it's turned on (according to this Apple Support page and my personal experience). That means if any of your other devices are lying around, they will automatically connect to your iPhone's hotspot using iCloud.

tl;dr: Other devices tied to the same iCloud account might automatically be joining your iPhone's hotspot network.