It's real. There's also a "yellow flag" and "red flag" style warning. I imagine if need be, we can AOB around that someday and see if it works.

Jarly would you explain what yellow and red flag? yellow as warning and red as the actual ban?
 
last time they implemented this people which play normally would also get effected..

all i can say is  that they are indeed testing stuff as they are  next to none  actions  were  taken during this pvp season...

These stuff in the game since long time, months ago a lot of people recieved the messages for no reason (remember back it was a big error in the game). I wouldn't worry about anything, if you don't get reported by other users PD won't start an investigation and the system won't be able to auto-detect cheaters.

It's an old experimental feature, like people have already said, nothing to worry about.

PD have tried numerous things to prevent hacking but they can't. I'm pretty convinced they've given up by now. But even so yeah, keep a low profile just to be safe, since mass reports might lead to PD actually taking a look.