In Cantonese 'Chow' with the 2nd PinYin intonation means fry for eg. chow
meen(fried noodles) or chow farn(fried riced)
In Mandarin it's 'Chao' with the 3rd PinYin intonation. In other Chinese
dialects from the south like Fujian/Hokkien or TeowChu it's more like Char.
It (the pronouciation) varies all over China depending on your dialect
group. My guess is that the Cantonese, whose cuisine is probably the best
known & travelled of all the Chinese cuisine outside Asia is where the
term/word "Chow", as it exists in American English is derived from. The
Cantonese dialect from southern China (Canton/Guandong province) is the most
prominant in that area. It is also the main dialect spoken in HongKong & due
to HK's historical ties with the UK & from there onwards, to the rest of the
Western world after 1945/WW2, i would assume that's where many people picked
up on the term/word "Chow". I remember seeing many Technicolor American
movies set during WW2 where sailors would often use the word "Chow" meaning
food or to eat. Perhaps the merchant navy & sailors did popularise the word
"Chow" from their many stopovers in HK or Asia where Cantonese is still
quite dominant. Or maybe it has an earlier entry into American English with
the International Settlement in Shanghai.

From a Chinese person's perspective, it's easy for a Chinaman to read a
written Chinese character or word like Fry as in "Chow or Chao" but to
understand each other's spoken dialect is not easy when it is pronounced
differently, sometimes with vast pronouciation differences depending on
where you're from. That's why Mandarin is the official spoken tongue in
China. Even this has regional differences esp. from the north to the south.
A typical example would be to hear someone from Beijing & compare this to
someone from lets say coastal Shanghai & again compare someone from maybe
the south western province. Anyway.... i'm getting off track here & it's on
hell of a history lesson.

DC.