In your opinion, when does a discussion become an argument?

I was on a 3 way text today with two people who are both former coworkers and friends of mine. The discussion was about politics, and one of the friends was just putting out some opinions, and the text discussion between me and the third person was a lot of back and forth, each of us giving our opinions and disagreeing with the other. The discussion stopped for a while, as I was having lunch with some people and my friend on the text was at work. In the evening, she texted again and I responded, and then I decided I was going to end it. I told her I am going to stop arguing now and will no longer respond, and her response was that she didn’t consider it an argument, she considered it a discussion.

To me, it was an argument but I may be incorrect. It felt like an argument to me. When does a discussion become an argument, in your opinion?