Richard, you are obviously very well-informed and very experienced in this so I hesitate to say this ...
It's perfectly reasonable to ask the question - that's the point of the forum. Both American white oak and the European oak vary significantly in character, and that variation carries through to converted and seasoned timber. In both cases, one example of one type can be markedly different to another example of the same type, so two boards of European oak from different trees could be similar, or quite different, all depending on a variety of factors, e.g., climate, soil type, growing altitude, genetic variation, and so on. So you might have an American white oak board that, at a casual inspection (just looking and handling the sample), appears to be essentially the same as a board of European oak. On the other hand, two similarly randomly sourced boards, one an American white oak and the other a European oak, inspected in the same way as before may seem to be very different to each other, but then again the same might be the case for two American white oak boards, or two European oak boards.
Given the information about variability described in the first paragraph, in my experience it's not possible to say that all American white oak boards have broadly easily identifiable characteristics (through a superficial inspection), that make it easy to distinguish a sample from boards of European oak, for the similar reason that all European oak boards also have broadly identifiable characteristics that are distinct from the American white oaks. Essentially, the superficial characteristics of both types tend to overlap one another ... in each each broad type some are paler than you might expect, or softer, or denser, or are harder to work, or easier to work, and so on.
More often than not, given two samples of the different oak types to identify, simply tossing a coin to make your choice is quite likely to be as reliable a method as carefully looking over the wood in front of you before choosing, ha, ha. Slainte.
