It's weird how some medical conditions are seen as inherently comedic. Tinnitus is one. Gout is another (apparently it is *amazingly* debilitating and painful). I guess we can't blame people who don't have these things for thinking they're funny ... For a lot of people, tinnitus is something aged crotchety grannies go on about in comics while holding massive trumpet-shaped hearing aids to their ears.
It's probably out of ignorance though: I suspect they think that tinnitus is the ringing you'll get for a day after the concert, and so their message is "oh yeah, it's so worth having to deal with ringing for a day". I doubt they know it can stick forever and be disabling.