I feel languages and cultures also gradually change over time and over a couple of decades it can be fairly different when you've been disconnected from it.
I was born in Hong Kong and lived there for 13 years, moved to the US and I'm now 40+. I was back in HK last year and although didn't have problems understanding people in Cantonese for the most part, there were situations like calling a restaurant (to make a reservation) where I absolutely could not understand the waitstaff's Cantonese. After 30 years I still consider myself more fluent in Cantonese than English but language and culture had evolved in HK so much that the way younger people talk, especially on the phone where it's harder to hear, is almost completely foreign to me at this point.
That is true of all languages, but I think that Cantonese has a particularly high change velocity in terms of vocabulary and pronunciation compared to, say, English.
I think this is because Cantonese speakers tend to read and write in Modern Standard Chinese (more like written Mandarin) and so are much less anchored by the permanence of text. Additionally, Chinese characters provide even less guidance on pronunciation than English spelling. In this landscape, Hong Kong's small media ecosystem is a fertile breeding ground for new language.
I know a guy whose mother came from italy to the US when she was young. He went back some Family over there. He was told “you speak Italian well, but you sound like my grandmother”
Same thing happens in the US too —- at least in the north east. If you go to New York, northern New Jersey, Boston or even Chicago, people in their 40s and younger don’t often sound like their parents; there’s little to no accent.
I work with a younger guy from the south and he definitely has an accent but that could be an anomaly.
This is from 90s. Tamilians in Sri Lanka were fighting the government. This is well known. Many of them escaped and came to India.
One of my Tamilian friends who lived in Delhi all his life went to visit Chennai. He was asked more than once if "he was from Sri Lanka" due to his accent - which was probably not Sri Lankan Tamil accent, but unfamiliar enough to get them thinking.
I was born in Hong Kong and lived there for 13 years, moved to the US and I'm now 40+. I was back in HK last year and although didn't have problems understanding people in Cantonese for the most part, there were situations like calling a restaurant (to make a reservation) where I absolutely could not understand the waitstaff's Cantonese. After 30 years I still consider myself more fluent in Cantonese than English but language and culture had evolved in HK so much that the way younger people talk, especially on the phone where it's harder to hear, is almost completely foreign to me at this point.