We shouldn't necessarily regard 5 as the correct output. Sure, almost all of us choose to make division higher precedence than addition, but there's no reason that has to be the case. I think a truly intelligent system would reply with 5 (which follows the usual convention, and would therefore mimic the standard human response), but immediately ask if perhaps you had intended a different order of operations (or even other meanings for the symbols), and suggest other possibilities and mention the fact that your question could be considered not well-defined...which is basically what it did.

Correct based upon whom? If someone of authority asks the question and receives a detailed response back that is plausible but not necessarily correct, and that version of authority says the answer is actually three, how would you disagree?

In order to combat Authority you need to both appeal to a higher authority, and that has been lost. One follows AI. Another follows Old Men from long ago who's words populated the AI.