It doesn't even need to be recovery...
... technology is a right tell-tale.
A month or so ago I was on a work trip abroad. We hired a car. The driver got the passenger (both more senior guys) to connect his phone to the car entertainment system so the phone-based SatNav audio would play through the car's speakers. I hadn't been paying attention from the back, until I realised, staring us all in the face from the entertainment system screen, was an obviously porn-site URL "http://porn.im.[whatever].xvideos.com/[whatever]" in 32-point text! No-one said a word, but it was a couple of excruciating minutes before the driver pressed a button beside the screen and made it go away.
Until now, I'd assumed it was just some recently-cached link on the phone - but I suppose, just maybe, it had been left on the hire-car system by a previous hirer? (I'm not familiar with excess consumer tech in cars)