Thanks a lot, I did not know about either. But yeah, short of having had logging set up ahead of time, it doesn't seem like I can get much more on the incident unfortunately.
Some more granularity in Android's data usage warnings, with maybe some sanity check presets (like a single app using up over 1gb in the same day or something) would be an easy and relatively painless way to avoid these, but I don't think there's anything more than the xgb over 30-day periods thing unfortunately.
Oh well. Hopefully it was a fluke. Day 1 of my monthly data allowance this happens, and my carrier are absolute dicks with their pricing for additional data. Ducks to be me