Rather sneakily, "sapere" in Italian can mean "to smell" or "to taste" as well as "to know". I think that this how it can also be used for "to seem" -- similar to English phrases like "this smells like a scam to me". (wordreference.com tells me that, as in the English equivalent, this sense of "sapere" is an informal usage.)

probably just something to memorize. Mi sa - it seems to me.

literally: To me it knows

I had the same thought and too would like to know whether subjunctive would be better here?

if things are not certain you use the subjunctive.