So what if it's "poly behaviour" or not? You said you two broke up... how did you say it?
The plan was to break up when she was ready to move on.
There's your answer right there.
Of what use it is to you to take this situation you helped create and are continuing to enable and put it in a box and call it "poly"? If it helps keep you in your comfortable denial that your partner "really is poly after all" despite the fact that SHE TOLD YOU SHE IS NOT REPEATEDLY YET YOU REFUSE TO ACCEPT IT (did I say that or just think it out loud?), then you have my permission to say this is "poly behaviour". After all, I heard that "language is fluid", words can mean anything we want them to mean anytime we want, and no one owns the word "polyamory", "my poly is not your poly", "there is no one true poly", "there is no one right way to do poly", etc. etc. etc.
There was an old couple in New Jersey who decided to drive cross-country in their car. Both were almost legally deaf. About 10 miles away from home, the burglar alarm for their car door got stuck in the "on" position. They drove all the way to San Francisco like this. You could hear them coming for miles. The alarm didn't seem to bother the woman at all; she thought it was sort of pleasant. Near Chicago, she said to her husband, "It sounds like faraway bees on a summer day."
Her husband said, "WHAT???"