I'd say the perception of Korean students being "more polite" (generally speaking more polite than students in South Africa, Australia, USA, etc.) is from their interaction with Korean teachers. Around my co-teachers, the students always followed a certain level of politeness, but around me, that usually dropped that (more so in middle school than elementary). I'd still say that overall they're more polite, but when it's just me in the class my experience is more comparable to teaching in South Africa. Some circumstances point towards this coming from friendliness or comfort level around a foreigner, but I imagine sometimes it could just be outright disrespect. Either way, it's not easy to demand the same level of respect a Korean teacher gets from the students - not that it's not possible or inadvisable - simply that if you're new here and you feel the discrepancy, it's best not to assume it's because the kids don't like you.
And never mind "Yes, it didn't" - a popular South African expression is "Ja nee", which is Afrikaans for "yes no"...