Standard Windows 10 can consume over 2GB of RAM at idle. Ultralight versions typically reduce this to under 1GB, making it ideal for systems with limited memory.
Someone took the official Microsoft build 19045.5198 (64-bit) and ran it through a customizer tool (like NTLite or MSMG Toolkit) to remove Windows Defender, Edge, Cortana, OneDrive, the Windows Store, and sometimes even core services like Print Spooler or Windows Update.