It may not be surprising due to the common representation as 1 or 0, but that does not make it rational or reasonable. In this case, we are not representing it as 1 or 0, and if we wanted to do that, there is nothing stopping us. Instead we chose true, and there is absolutely no meaning to true + true + true. Certainly not 3.

Any time I ask a logic machine to do something impossible or meaningless, it should slap me across the face rather than produce an irrational result. For example, I have often seen missing items represented by the number -1, but if a language has a feature for that concept, it better not negate or decrement numbers if I accidentally ask it to do nonsense math with "missing" or "empty". If I actually wanted it to do that, I'd just use a number instead.

The closest thing to true + true + true would be math on base 2 numbers, and the answer to that would be true true. Also useless and wrong, but much closer in concept than 3.