Yes, he once taught illegally and Scottish accent is hard to understand for English learners.

Yes, well we know who started that malicious rumour- two ex-posters who are probably still posting. Let me tell you this, when it comes to native-born English accents I am a good judge and I do have trouble understanding, say men from Devonshire and many parts of the North, also some American accents, but the Scot you are talking about speaks the Queen's English and is a pleasure to understand, having spoken to him several times.

From time to time all Westerners will be accused of being difficult to understand if the accents they are used to are their own Chinese teachers, or even bloody Russians.