I got this for the first time (or at least the first time that I was paying attention). I tried asking my friends that play about it, but none of them were online to tell me that they didn't know what it was. So I found this thread and spent about an hour reading through the whole thing cause I enjoy wasting time.
I also got it after wearing the same equipment for a while. I was definitely at the bottom of the scoreboard with 1 kill 7 deaths. I doubt this has anything to do with it, but it was shortly after I made the first kill in a round on Battle. It also wasn't long after I dedicated a main account (never got it before that).
Since chadz said it's an attempt to improve role play, it would make sense that wearing the same equipment set is a trigger. Either that or more knowledge about your equipment is near useless unless you get it on the same equipment multiple times.
We've also been told that there's a random chance and level affects it. My guess is for every level, there's a set number of points (quite possibly just one) where the random chance determines whether to activate or not. If it does, it could just check for other components of the formula, and if everything works out, sends you the message.
I've got some questions for anybody who's had this message and is willing to answer them:
Have you ever gotten this message more than once in a single level? (if so, how many times max?)
Have you ever gotten this message while wearing something other than your default inventory? (betting somebody has, but I was wearing default)
For those that have gotten this while switching armor recently beforehand, do you often wear the armor that you got the message with?