What is this/what does this mean?

I don’t really have a woman in my life to ask about this so I’m just gonna post it here. So my boyfriend and I were chilling in his car and for the first time he fingered me but I don’t think he necessarily did it right, I think he was just going in the one same circular motion the whole time and felt a little bit like he was pounding against the walls of my labia lol like I don’t think he was doing it right which is fine Bc it was the first time I’ve been fingered so I don’t have much to compare it to. But after I just eventually told him to stop then I felt really wet a few mins afterwards after he took his fingers away and when I got home I saw this. What is this Bc I don’t believe it’s an orgasm haha. Apparently according to my chart I’m supposed to get my period in 4 days. Also these undies were brand new may I add.