Edit:
中国人:你的中文是[在哪里]学的? indicates the question is asking 'where'
中国人:你的中文是[怎么]学的? indicates the question is asking 'how'
中国人:你的中文是[从哪里]学的? indicates the question is asking 'from what source' And sources are not locations -- For example: from books, from classes, from T.V.
'From what source' = 'with what methods' --> 'how' you learn
When the Chinese person asked '在哪里学的' but claimthen claimed he was asking "how" he should have said 从哪里 instead of 在哪里
'在哪里' refers to 'what location' e.g. Hong Kong, Beijing, Shanghai.
'从哪里' refers to 'source' e.g. books, classes, the internet.
Does 「你的中文是在哪里学的?」mean “How did you study Chinese?” or “Where did you study Chinese?”
It means “Where did you study Chinese?"