What's the upload from your system that's streaming it out? You've hit more on a capacity issue from your internet it sounds like.
What's the bitrate of the media being played to?
That's simply not quite the case. You don't count a full file when you seek around as they are range requests. Google doesn't publish specifically how it works other than you have a 10TB daily quota.
You can test it pretty easy with running a mediainfo on a large file repeatedly and if the whole file counted, you'd evaporate the quota pretty fast.