When the Strava heatmap issue came to light i recall seeing many tracks on military runways and wondered, "who's out there doing laps on the tarmac? So this makes sense now.
No. People in deployed areas often run on runways. The Garnin watches aren’t transmitting and they aren’t connected to Strava.
At least half of Garmin watches are connected to Strava. They do transmit through Bluetooth, ANT+, and/or WiFi.
It's not a direct connection. You must log into your Garmin Connect account and configure it to push to Strava.
Apparently a lot of people in the military upload their runs to strava. If there are a bunch of people uploading the same route, it will show up on the strava heatmap. This has previously caused secret locations to be revealed[1], but they are probably being more careful about this now.