It's not. Something went wrong with the installation - my guess it's the installer got corrupted by something like antivirus software, targeting part of the data as malware that caused it to accumulate corrupt data till it bloated. Read somewhere that someone had this problem with another game from Itch. I'd say to try to download it again after removing the old one and give the website a 1-time pass for antivirus not to check (risky but that's the only way to prevent it meddling)