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"Actually not precisely true. If the parent with A gene also has O recessive, then half the children can be O. If parent is AA (with both genes A), then you are correct."

I can't argue with you. I was just paraphrasing Professor Stephen Oppenheimer from his book, Origins Of The British, on page #353-354 when he says:

" Our expression of blood groups in the blood typing test depends on the genes we get - one from each parent (our genotype). Blood group A is dominant, which means that the result of our blood test (our phenotype) is group A, whether we get one or two A genes from our parents, Group O is recessive, which means that we must receive both our parental genes as O to have an O blood group phenotype. If one parent gives us a O and the other gives us an A, we will test A.

Have I misinterperted his statement?

...which means that we must receive both our parental genes as O to have an O blood group phenotype.

The ambiguity in this statement is that we only receive one respective blood group gene from each parent. Another way to think about this is that the O blood group would have been eliminated early on if it actually required two O type parents to propagate it.

Have I misinterpreted his statement?

You've extrapolated an untrue statement from it.

AA + OO = all kids AO, having A blood type is true.

BUT a person with A blood type can have an O recessive. Thus AO + OO means chances are half the kids will be AO (A blood type with O recessive) and half the kids will be OO with O blood type.

It is possible for an A blood type parent to have O blood type children.