Document without charset

Reference:
http://validator.w3.org/check?uri=www.unics.uni-hannover.de/nhtcapri/test.htm

The validator says:

| Encoding:   utf-8
| Sorry, I am unable to validate this document because [...]
| it contained one or more bytes that I cannot interpret as utf-8

This is not helpful!
Why does the validator assume UTF-8 in the first place?

IMHO it would be more helpful
(a) to say "No Character Encoding Found!"  or
(b) to take a charset that fits (in this case ISO-8859-1).

But *do not* assume UTF-8 if this is impossible (and then say
that it is impossible).