I'm uk and I use smart, in fact I see it as slightly different to clever and intelligent. You can be street-smart (streetwise) for example. It doesn't mean you're intelligent.
Sure it is used here, though as you say, in a slightly different sense, and to to a lesser extent, than in the US, (though it's probably derived from US usage).
But of course the point is not to exclude ׳smart׳, it is to allow for some more probable UK equivalents of חכם
Pealim is a bit confusing here because it doesn’t show הייה, it shows היה in the imperative section, but ata narrows it down to masc. singular, so heye is correct.
Haya, also spelled היה, is “he was”.
I say “also” because heye, spelled with niqqud, is היה.