A questions counts as unanswered until is has (at least one) answer(s) with positive score or an accepted answer.
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We mix semantics of "answered" here; do we mean the OP got an answer, or there is an answer-type post? The naming of the "Unanswered" tab assumes the former meaning which I think is fair.
I guess from the scenario and the approximate timestamp that this happened between 2016-07-21 18:07:57 and 2016-07-21 22:01:15 UTC. Please mention this information explicitly, it's important!
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When you use the “full” website:
If you have less than ...
< is also the starting character of any HTML tag - which a subset of is allowed in markdown.
As such - it isn't escaped by the parser - and your browser thinks that everthing after < (until a > is reached) is a tag. So isn't shown on the page.
Solution? When posting math, use math formatting, as in the edited post.