https://orgmode.org/manual/Math-formatting-in-HTML-export.html
(131)
Please note that exported formulas are part of an HTML document, and
that signs such as ‘<’, ‘>’, or ‘&’ have special meanings. See MathJax
TeX and LaTeX support.
The link is broken however.
http://docs.mathjax.org/en/latest/input/tex/html.html#html-special-characters
Usually, it is sufficient simply to put spaces around these symbols to
cause the browser to avoid them, so
... when $x < y$ we have ...
Though I am a bit surprised that Org did not replace characters to <
and > during export. Perhaps, it is possible to define a filter.