I called TUBS and asked about the dumpsterbag. Apparently the dumpsterbag at the apartment complex down the road is the one that called for a pickup, and the pickup guy mistakenly got mine instead.
On one hand, it's a relief, at least for me. Of course, for whoever paid for the pickup at the apartment building, it may be a bit of a headache, particularly if the management company gets pissy about having a dumpsterbag on the lawn in back (they really shouldn't-- it's out of the way of pretty much everything-- but sometimes they can be cranky about stuff, ya know?).
It's entirely possible that they may send me a new bag since I wasn't done with this one. I don't really need it right now: if they just don't charge me for the pickup, I'll be more than happy as that's 95 bucks that I'd otherwise have to pay. And really, this one was pretty full of heavy stuff like concrete bags and construction crap, so it's not like it was a huge waste.