The occupants of the costume are laboriously dragging themselves back to the shop after being trapped in the costume for some unknown amount of time. The costume is shown to be patched and likely in a poor state and the shop isn’t surprised by what they’re seeing as it’s happened before.

The joke is basically imagining whatever hijinks happened to the people in the costume for them to be essentially crawling back into the store, and also how this sight has happened often enough that the shop isn’t even surprised.