It doesn’t mean they’ll all be major kaiju we know from classic Godzilla movies, they may be largely generic creatures like the ones Godzilla fought in the previous film, but maybe there’s more going in Godzilla: King of the Monsters than we know.
Ken Watanabe’s character appears to say that 17 different creatures have been detected, and he clearly expects more.
One other interesting piece of information we get from the new clip is that the monsters that we have seen previously getting all the spotlight, Godzilla, Ghidora, Mothra, and Rodan, aren’t going to be the only creatures in the movie.