I tend to agree with your guess, but we don't have
any archived definitive Peter D'Adamo quotes on it.
Several ingredients would pass - since us type O's
are allowed wheat-free tamari, beer (made with malt)
and some yeast breads.
"Natural colour" and "vegetable extract" however
are too vague to compare.

It shows up from time to time in specialty stores
in the US - The Marmite version seemed pretty salty.
Is there a trick to how much to spread or something?

Is it a source of B vitamins? That could be a nice plus
in the near-absence of grains.