Is ‘how’ here necessarily used to ask about the means of transportation used to get to the party? No. In a different context, could I answer ‘I wore a jacket’. Yes. Depending on the context of the question, some possible answers to the question are I got a ride with John. (What was your means of travel? Without additional context, this would be the default meaning) I got an extension on my project. (How did you have the time to go?) I went stag. (Who did you go with?) I wore the Batman costume from last year. (How were you dressed?) Susan invited me. (How was it that you were you allowed to go?)

To me the question is talking about transport. What did you wear to the party/ How did you dress for the party are talking about clothes.

- How did you ... = Transport question. - How did it ... = Opinion about the party question. And yes you can answer that, if asked what you wore to the party.