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.

I should also mention the pros and cons of using CHD files for PS2. Pros include smaller storage space, possibly faster loading in some emulators. Cons might include the need for decompression on the fly, which could affect performance, but modern emulators handle this well. Also, compatibility issues with certain games if the original data isn't exactly replicated during conversion.

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.