Why does this regex match?

I am a bit puzzled by a regex match:

In the above screenshot, the regex matches if I have a no-break space between "81" and "cm". I does not match if I replace the no-break space with a normal space.

This is the regex:


As the name suggests, I want it to match when a date range or numerical range is connected with a dash other than an en-dash.

Why does it match here? What did I do wrong?