Understanding American English Vs. British English?

Is it harder for Hong Kong ESL speakers to understand American English than British English?

Hong Kong people are using Chinese basely, English as a second language. English will be an official language for the Official documents or legal (Basic Law Promotion Steering Committee). Now a day, under the education of Hong Kong, students needs to be learned biliterate, it will be Chinese and English, also trilingual speak in Cantonese, English and Putonghua.

Hong Kong as a British colony from 1841 to 1997, at that time all government documents are also English-based, while the education of English must be British English too. In general primary and secondary schools, we did not pay attention to learning which kind of English, but it was wrong
First of all, British English and American English have the most obvious difference is the vocabulary, the two kinds of English vocabulary are greatly different.
American English will call the 'photocopier' to 'Xerox’, in British English you can clearly know the object is a machine to copy paperwork. If you are not American, you don't know Xerox is for what, American call it 'Xerox’ is because of the brand of the photocopier. (Voice of America) Another example, 'apartment' will use in American English, in British English will call 'flat', those words do not have a big difference, but they're giving a different feeling.
'Apartment' is an individual room in a building, and some of the facilities are shared with other people, while 'flat' means a suite house. Although the apartment also contains the meaning of the suite house, but the flat can shrink the meaning of the object, to avoid misunderstanding in the communication.

Talk about grammar, in Britain English will use present perfect tense in the sentences, and American English will use past
For example, the word 'turn' in Britain English, it won't have the 'r' sound and sounds like /tɜːn/ , but American English have a clearly 'r' sound, it will become /tɜrn/. (Anglo-Link)

In British English, the 't' sounds /t/, whether it is in the middle or at the back of the word. But in American English, sometimes 't' will sound 'D'. The word 'water' in a British accent, it can hear the /t/ sound, will like /ˈwɔː. tər/. American accent will make the /t/ sound become /D/, so it will change to /ˈwɑː. t̬ɚ/. (Anglo-Link)

In Hong Kong, English is not the main language, in the daily conversation, whatever we use American English or British English, both can convey the information, there are many people do not know which kind of English that they learn or use. The most common is learn British English at school, but after time and culture going, it will be inserted American English in British English.Sometimes ask people why they use English within British English and American English, most of the answers are more fluent or often heard.
Many of the Hong Kong people do not tend to which kind of English, for the most common word 'colour', we will write 'color', one of the reasons is Microsoft Word will correct us, and the software will turn British English into American English, the correction will be changed people wording