"Just decided" =/= decided today. They decided months if not years ago, after months of negotiations with local authorities. Don't look at plants opening now to judge the current administration. Look at it 2 years from now.
I don't know - the article specifically said Honda will produce the cars "to avoid potential tariffs". I don't think the Trump tariffs were in place "years ago"...
Of course, a marketing line to fit the current situation (and curry favor with the current vindictive administration) is easily added/updated at press time.
This does not mean the making of the deals and building the factory had anything to do with it at the time, but stating that those past decisions also have benefit in today's situation is not surprising.
It also does not mean that this has anything to do with the actual reason the deals and investments were made years ago. As you point out, those deals & investments years ago couldn't have anything to do with this week's tariffs.
