Wait, PCSX2, a popular PS2 emulator, uses ISO files. Maybe the user is using an emulator that now supports CHD, or there's a new tool. Alternatively, maybe they're using a frontend that organizes CHD files, but that's more relevant for arcade emulators.
Also, check if there's any recent patches or updates in the emulation scene that affect CHD usage on PS2. For example, PCSX2's handling of CHD files, or maybe a new emulator that's beta testing but shows better performance with CHD. ps2 chd roms upd
Alternatively, the user might be referring to a "rom update" in general for PS2, but specifically using CHD format. Perhaps they found out that some PS2 games have updates from their original release that are distributed as CHD files. But I'm not sure. Alternatively, maybe they're referring to a tool that updates CHD ROMs, like a new version of the CHD tools or an emulator update. Wait, PCSX2, a popular PS2 emulator, uses ISO files