it is called a memory dump. it is everything that was in the memory space of your PC at the time of the crash. So they can see what enviroment and other programs and memory usage was going on at the time of the crash. without which they are just guessing what program space the crash occured and why.
There's some rules in crypticerror about when it takes a full memory dump of the process, and when it just takes a short one of some particularly interesting parts. I don't think they ever explained precisely what causes this.
It's supposed to do that, anyway. They need that data to debug some issues.
In general we only take a full dump the first time an error happens or every X days (60 right now I think). Between those it sends minidumps that just have the process stack and so are so much smaller you've probably never noticed. So congrats, you either found a new or very rare bug!