The percentage is packet loss (or apparent packet loss anyway) so if it exceeds 2% on the last hop you get a failing grade.
It is not typical of cable to fail, but indicates something between your keyboard and comcast is not responding in a timely manner.
if you computer or router is set to not respond to pings you will fail, if it is too busy to respond due to other tasks you will fail, various clock errors and you will fail, an extremely busy router or one set to discard pings and you may fail.
That test works best after a clean boot with as few other things running as possible (everything from email and undate checkers, to remote backups, streams, and chat should be shutdown) your systems must be set to respond to pings, and once you click START remove your hands from the mouse and keyboard and do NOTHING until results are in.
BTW you can safely share the graphical test results
which are much easier to read and interpret