That shot could certainly be showing some new power Godzilla's going to have in this one, since the energy effects were blue rather than yellow after all. And Yamazaki's talked about Shin Godzilla being one of his favourite Godzilla films before, so with how much influence GMK had on Minus One, I could see him working a bit of Shin influence into this one by giving Godzilla an ability we've never seen before. It looks like it's going to be a cool sequence either way!
Besides that shot though, I'm mostly going off of how often he floated the possibility of Godzilla fighting another monster in the sequel, before this was announced, as the main reason I'm expecting one to show up in this. That's why I'll be interested to see if they confirm that in any more trailers, or if they'll stick to just showing Godzilla as the only threat in the film (whether he turns out to be or not). But in terms of this teaser alone, even if Ghidorah's in the film for sure, I'm not entirely surprised they still wanted to focus on Godzilla here. The trailers for G'14 focused almost entirely on Godzilla being the threat in that film, with only one or two shots of the MUTOs, and even some character's lines edited to make it sound like they were talking about Godzilla when they were really referring to the MUTOs. Then the movie came out and it turned out to be almost a "stealth Showa film", with Godzilla as the good guy and the MUTOs driving the story more than he did. So they could totally just be wanting to have this teaser do the job of letting people know the movie's coming but not give us a big reveal of another monster just yet.
Or they could continue to have more trailers that only feature Godzilla because Godzilla's the only one in the film.

Pre-release it's a lot easier to say "maybe they're just not showing Ghidorah yet!" than definitively proving he's going to be in the movie without them actually showing or announcing it.

Still, I'm definitely thinking that's what's going to happen, but regardless I'm hyped that we're getting a sequel that, even with just this little bit they've shown, already looks like it's going to be so good!