Given the tatty nature of the bike locked to yours (which I assume is the Peloton?) I think you may be being targeted by bike thieves. It's a fairly common tactic to lock another bike to the intended target, then come back and steal it later.
Either that or the owner of the other bike is a weapons grade moron.
I've been thinking this...and I'm quite scared what the situation will be when I check later. Although, given the other bike was also secured with a separate chain lock (obscured in the photo), I'm hoping that the person is just in fact a bit of a bellend.
Given the tatty nature of the bike locked to yours (which I assume is the Peloton?) I think you may be being targeted by bike thieves. It's a fairly common tactic to lock another bike to the intended target, then come back and steal it later.
Either that or the owner of the other bike is a weapons grade moron.