It comes across pretty badly in my dialect of American English to turn adjectives about people into nouns. For example, "I saw a disabled on the bus today" or "a visually impaired" or "a Chinese" without "person" afterward would all be really weird phrasing, and if you were otherwise fluent in my dialect it would imply that whatever you were about to say next was likely to be pretty clueless about that group.

BUT I wouldn't apply that inference to someone with a foreign accent, even a British accent. It's a fine point of style that I can't assume will translate across dialects. (For example, "I saw a German on the bus today" would be much less weird than "a Chinese" to anyone speaking my dialect. How do we know? We just know.) So here I think mbrookes has the wrong idea.

All I can say is thanks for taking the time to write this. For the life of me I could not figure out what did the op do wrong.

I guess their complaint is that the phrase "visually impaired", rather than "people with a visual impairment", or even the less respectful "visually impaired people", sort of makes it sound like the people he spoke with are defined by their disability.