

Before virtual memory was a thing, almost all memory was accessible.
Virtual memory has nothing to do with whether 0 is a valid address. You can have a CPU where it is valid, or one where it isn’t and you’ll get an access fault if you try to access it. You can also have virtual memory where page 0 is mappable, or not.
I think the author knew that, based on the later points so it’s probably just bad wording. Interesting point about wasm too!
Small nit:
The 128-bit capability (actually 129 since there’s a tag bit) includes the address. It’s 64-bit address + 64-bit metadata + 1-bit tag = 129-bit capability.