The author assumes that if the speech wasn’t inflammatory, then it wasn’t inappropriate. This overlooks the possibility that the speech could have been inappropriate for other reasons.

The author’s position is that we don’t have evidence the speech was inflammatory. So what’s possible in the event the speech was inflammatory doesn’t matter. The argument concerns what a non-inflammatory speech would imply.

We don’t know what the president’s side in the dispute is, and we don’t know whether the author favors it. In addition, the author doesn’t rely on the president’s standing as support for the conclusion.

The author does point out that Riley has been in a feud with the president, but that doesn’t imply that Riley has anything to gain from people thinking the speech was inappropriate. So the author’s conclusion is not based on the idea that Riley has something to gain.

Whether Riley’s feelings about the president are justified is irrelevant. The issue is whether the president’s speech was inappropriate, and whether there are other ways for it to be inappropriate besides being inflammatory.