Are you by any chance using screen bottom boards? If so, bees will clump on the bottom because the open screen confuses them. After a few days or so, they figure it out and go in through the entrance.
As Irwin said, there are some internal workings going on within a new package install that occupies them for a few days or so. Try not to worry, all should be well.
I'm modifying my post because I realized you said the clump was on the ground but will keep the info I mentioned for anyone with that issue (bees under SBB).
Who knows for sure why they were clumped on the ground. Possibilities: syrup soaked, disoriented...
It happens.
...JP