So thas exactly why I brought up Plato. And I think the song and lyrics do an excellent job summarizing,

Your title asks whether we can infer intelligence. Verbatim. The answer to that is, again, yes. We do it constantly.

You cannot directly observe my intelligence or thoughts. You observe my behavior, language, problem-solving, etc., and infer intelligence from those outputs. The same applies to a machine.

The Chinese Room raises a different question: whether apparently intelligent behavior is sufficient to establish understanding or semantic content. That is not the same as asking whether intelligence can be inferred.

Saying "it's just following rules" doesn't setkle that question either. Humans are also physical systems whose cognition is implemented through mechanisms. The existence of rules or mechanisms does not itself show that intelligence is absent.

So becaus your question is specifically "can we infer intelligence?", yes.

Now, If the question is "does intelligent-looking behavior prove semantic understanding or consciousness?", that's a different and much harder question. But most importantly, it's not the question you asked.