I didn't. I never encountered the term.
I DID know early on I loved more than one and before I married Maca I was in open relationships for years.
But-I didn't realize there was a word for that.
When I learned, I was already well on my way to destroying my marriage with Maca.
Thankfully-we were all willing to educate ourselves and work together to find a functional family solution.
But-I do have friends who are poly that came to it single or mono and moved into poly dynamics after establishing an agreement with their current partners. So it does happen-but all too often, people don't go searching for information until they are in crisis and need it.
You are fortunate that your wife found information and choose to address that with you before getting herself into a messy sticky disaster. That speaks highly of her ethics and personal responsibility.
"Love As Thou Wilt"