I'd be amazed if #1 washed in court. By connecting to a swarm that is distributing copyrighted works without the copyright holder's consent you've demonstrated that you have intent to pirate the material. Besides even if you argued that you got a few chunks of the file from the copyright holder (or a party acting on their behalf) you will have downloaded other chunks from others (and possibly uploaded some of them back to the rights holder).

#2 I'd put down to a random bureaucratic fuckup rather than an inherent issue with the detection system. I know a couple of people who've had letters from their ISPs regards these activities and they have said that they were accurate.