I actually agree that it is a weak argument to say that his tweet was witness intimidation, since the witness would have no way of knowing about the existence of the tweet while she was testifying. It obviously wasn't meant to change her testimony in any way. Though I'm curious wehre you get your list-of-three from. I'm sure any court would, for example, rule that coercing a witness into not testifying would also count. This looks like something you made up on your own.
Witness intimidation would be a more appropriate term, by slandering witnesses to the entire country it causes other witnesses to not come forward. At minimum this is another example of unpresidential behavior from an unpresidential president without dignity.