Where and how is IMEI attached to Wifi uploads not using mobile carriers?

Here is the gist of the story.
Creep uploads photos of ex.
Ex finds out and registers a case.
The creep uses a wifi access point n a college he isn't registered in, using a new phone that doesn't have a SIM card in it, thinking no IMEI will be attached to it and wont use the 4G cell towers.
Somehow cops still catch this creep, by using they say the IMEI number...
But where was it?!
Can anyone breakdown …

access access point card carriers case college isn mobile mobile carriers phone photos point privacy sim sim card story thinking wifi