Well, that person seems to know you have a stream, and went out of their way to tell you that they reported you.
In order to trip the Squelch functions, or get GM eyes on it, it needs more than one unique report - can’t come from the same account. Chances are high that nothing will come of it, besides them getting their knickers in a knot and hitting the button.
Just telling you once is petty, but not technically harassment.
Unwanted contact is indeed harassment once you put them on Ignore. Please be sure to Ignore that person. That should also ignore any other char on their license (maybe Bnet account?) when you are on your char.
If they engage in actions to circumvent the Ignore then that becomes actionable Ongoing Harassment.
This article should give you lots of info on that, and tell you how to handle it.