That was certainly one part of the column, but not the only part.  Read the rest of the article.  Trump has accused Germany of currency manipulation, running an unfair trade deficit (whatever that is), accused Merkel personally of ruining Germany through immigration and on and on.

Of course, Trump can't be trusted.  Not only does he fire off his silly little tweet with little to no thinking, he changes course at a moment's notice for no apparent reason.   There is no coherent thinking behind his actions, no plan, nothing.  Just emotion-based reaction.  That is completely untrustworthy in the realm of international relations.