Ryan was a hot-blooded idiot, he knew that, but he wasn't a complete imbecile. Once he recognized what the skeletons were planning to do, he began to move away from the dungeon while he still was hiding underneath the snow.
"There is no mistake, they are being controlled… even if monsters might use Telekinesis, there is no way that they can have this much synchrony relying on such skill alone. Most likely, the bosses are in synchrony controlling them."
That would also explain that decision-making speed. Ryan didn't even kill one thousand of them, and the creatures had already decided to retort to big moves. Regardless, Ryan retreats to a hill where he hid his salamander, and from there, he saw the monsters marching around the dungeon and melting every single bit of snow. Not even ten dragons could have melted such a large area so fast, so it became even more evident that Ryan couldn't underestimate them.
