Its not about the shirt
People wear, say and do things every day that _someone_ is going to find offensive.
Sometimes that "someone" is going to make a fuss.
The question is what happens then.
What's happened here is ESA's seen a PR shitstorm coming, crapped its pants and sent Matt Taylor out to deal with it. Something which, as a rocket scientist rather than a PR drone, he is not equipped to do.
Here's what should have happened. One of those glossy talking head types up top at ESA should have got out in front of this and made the following statement.
"Good morning. Welcome to the press conference. We have some exciting new about the mission. Before I start I just want to touch on some stories that have been floating around concerning an item of clothing worn by one of the team last week. I have talked to that member of the team and am satisfied that the incident was a mistake and that the mistake will not be repeated. As project director I take personal responsibility for such matters and as such all questions about it should be directed to me personally. I regret in advance that since this is an ongoing HR matter I cannot due to privacy rules discuss the specifics of the incident nor the identity of those involved.
Now then. On with the press conference. Here is Matt Taylor."
And that would have been it. Done. This isn't rocket science.