Do you think Matthew felt that offended by the sea monster exchange or was he more reluctantly impressed?

I get the sense a part of him was impressed. He wanted to win her over amd he can empathise with her frustration that it isn't fair that she can't inherit. He says this to Violet that it is very harsh and he doesn't truly blame her.

Then getting to know Mary and see her softer side must have just been all the more rewarding, he first saw her sharper edges but there was so much more to her than that as in she loves deeply and is loyal and scared of being vulnerable