スマート (-na inflection, rōmaji sumāto)
What type of semantic shift is this?
Please see the titled question.
This is not a semantic shift nor are they false friends. In English, smart has several distinct meanings. It has been used for to look stylish for a long time. It is still used for this meaning, albeit less commonly and mainly in British English varieties. Using it for intelligence is more colloquial and has developed more recently (and is more common in American English varieties).
smart adjective (STYLISH) mainly UK
having a clean, tidy, and stylish appearance.
smart adjective (INTELLIGENT) mainly US
intelligent, or able to think quickly or intelligently in difficult situations.
The Japanese スマート has been derived from the original meaning. Of course, the Japanese language is changing as well, it is now also used for smartphones, just as it is in English.