I can't explain it either but I can confirm your observation. That folder is 11 MB in my system. I don't know how big it was originally (your post is the first that I knew of this) but clearing the Safari cache had no effect. I don't want to clear the Safari history because I want to keep it.

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365