That sounds like Akismet (our spam detection tool) at work flagging spam accounts/posts.
The thumbs down says Akismet disagrees with the account/post and the percentage shows how much it disagrees. the amount of time staff has agreed with the flag from this particular person. It gets weird when the person is a bot.
The main icon indicates the highest stat, in other words it is a shorthand for:
Do staff members typically agree with, disagree with, or ignore flags from this particular user?
In this case flags generated by the System user (not a real user, of course) are being disagreed with 100% of the time by staff, so you see 100% and thumbs down. Looks like the spam prevention is being a little over eager in its flagging?
Jeff is correct, if you place your mouse or hover on the thumbs icon, you’ll see an excerpt that explains what it means. And as Jeff said, flags generated by the System user (not a real user, of course) are being disagreed with 100% of the time by staff, so you see 100% and thumbs down. Which is what you see for some new members.