[@Isaac] I'd generally prefer new players to be around a while longer and build up trust before they introduce new plot points / encounters, especially without permission first. In this case, there are Gruzzers in the crossroads cavity, but not in numbers anywhere close to what you described. You could have had the Adventurer fight a few or even group of them without bringing in a swarm big enough to create a 'wall' which now must concern all the other characters in the area. It also doesn't make total sense because Ms Fortune already made a huge noise when she fell, which would have alerted the Gruzzer swarm already if it existed at the time and if the Gruzzers are violently aggressive, which they are not, instead being kind of bumbling and mindless.

As for 'why', I limited the number of enemies in this area because for the sake of progression we don't want everyone to spend more time in the crossroads or Temple of the Black Egg, but instead find and decide on a way forward. Maybe after Bowser rallies the two parts of the group back together with a few words like 'we should stick together', then decides on a path using the map and just forges onward leaving everyone else to follow him.

This isn't that big an issue right now because Gruzzers are weak and we have a bunch of characters in the area, so we could probably just include some fly slaughter in our posts before continuing and not, say, spend a full week on a new big encounter. But it would have been if you chose stronger enemies. So you don't need to change it this time, but consider your 'free ticket' spent, and please keep this in mind for the future.