Is OTHER wrong in the post ? POST : This happened one week ago, but today some developments came up.

Basically, the 31st, me and my girlfriend went to a party with some friends of mine. The party was organized by an old classmate, ex male bestfriend of my girlfriend. He didn't know she would came and when he realized they started talking and I left them alone to catch things up. At the end of the party she came to me and told me how she had never been so drunk in her life and she could have done something she would have regretted for life (but she couldn't remember what).

The next day, this old classmate asks her out, to catch up better. I'm obviously happy for her, since she hasn't had friends of her own for years.

The following Sunsay they go out, but, before he picks her up, she tells me she will write me all night in order for me to check if everything was going smoothly.

Then she writes me when he arrives and stop, nothing is written to me for the next 4 hours. I start to worry and to write her and call her: no answer.
Since I was worried I call her friend. He doesn't answer.
I call again my girlfriend and she answers:

Basically, when he arrived, he took her phone and told her that it was their night out so they didn't need the phone. During the "date" she asked him for the phone but he didn't let her. At the end, while they were driving back, she had his phone and saw my call, so she told him and asked her phone. He got angry and told her that I was toxic and overprotective. She didn't say anything and got home.

Today he writes her again, asking if she was still "at house arrest".

So my question is, since it's my word against his, am I the asshole for calling them during their night out? I'm obviously mad at him, not my girlfriend. 

Tl,dr: girlfriend goes out with old friend, promises to check on me, doesn't answer, I call him and he gets angry. 