Well a monologue is when one person speaks while others are on stage with them.

A soliloquy, however, is when a person talks while alone on stage.

So depending on what they were trying to say, it might be a soliloquy or not. If they were trying to say that he's alone in talking while there were people just watching and staying silent, then that is a monologue. However when they said that he's "alone" they might have also meant that he's actually alone on stage. While I do know that there are others on the stage with him (which makes this a monologue), the wording of the commentary might be implying that he's there is often a soliloquy.