Actually, the "== 2" would work right, it's just that the whole point of having an enumeration like PointHistoryBits is so that you don't hard-code enumeration values in your code. (Well, that, and the fact that the enumeration helps "comment" the code.)
So you should use something like this:
if ((e.Context.History & PointHistoryBits.NotDigitizer) == PointHistoryBits.NotDigitizer)
Or, a bit simpler:
if ((e.Context.History & PointHistoryBits.NotDigitizer) > 0)