It’s possible the “mystery” they refer to could be related to the identity of the hacker(s), how it got onto the routers in the first place, or the purpose for the attack
You posses extremely niche knowledge. Being catty because the headline doesn't suit your preferences comes off as fairly rude and pretentious. Good for you for understanding that the headline is misleading, but there are more relatable ways to say that.
Your reply reads to me as if you’re calling me disingenuous, which I can’t for the life of me understand. I’m not the author. I offered a possible explanation.
OpenWRT uses Lua for its web UI. The interpreter can be really small which works well for tiny embedded devices with mere megabytes of storage, and it's much safer than writing a web GUI entirely in C.