It is. Not a single time we saw Marin as an insecure person. She isnt perfect, but she wont hesitate. You can even see how different she act back when she saw Gojou making depressed face on Christmas and when she saw Gojou face after cosplay. Its very different. And its because someone wants to drag this series on to milk more content.It isn't like it came out of nowhere. She was feeling increasingly insecure and made a hasty assumption.
Well she didn't waste time and went for the kiss, so it's only fair 😏He didn't waste time with getting handsy.