Do you think it's more likely that they invented a unique id scheme that requires 50 bytes, or that they're using an overly wide datatype for ordinary UUIDs?
Like I mentioned, there are different UUID/GUID schemes using more than 128 bits publicly available already. You don't have to invent one. They may simply be using one of those with additional bytes reserved for future algorithmic changes (using first few bytes as a header to specify the algorithm).