Hmmm...where I live salt is heavily used in winter so seeing gaping holes in relatively new mufflers is nothing new to me...However, as you say in the video, your car isn't exposed to such conditions...
That's very odd...Looks almost as if it rusted inside out!
My stainless steel Genius Exhaust still looks new save for some dirt and slight wear on the exhaust tip.
Many short trips, not letting the exhaust get to full temperature will rust it out from the inside. Never gets hot enough to evaporate the condensation from cold starts. Water sits inside the muffler where it is raw steel and rust happens very quickly. Better to run it on the fwy for 10-15 minutes minimum. Get up to full temp and all the condensation out before shutting it off. If this isn't possible, then an all stainless system will last longer. It will come at a cost though. Expect to pay way more. The stock muffler is more restrictive and gets hot quicker than a free flowing muffler, hence it is better at burning the condensation out in shorter distances. Just watch the exhaust pipes of the cars in front of you at the stoplights early in the morning. They are cold and when the light turns green, water will pour out of the pipe as it takes off.