You can't really make that conclusion, you can only conclude the clientele is non-Chinese if food is bad but the restaurant is thriving, if the food is good then it's kinda hard to tell because many white people have refined their taste buds, at least in Vancouver.
It used to be a real turnoff for me because I thought it totally ruined the atmosphere, though now it doesn't really matter.
Sushi is not rocket science(well it won't be a problem even if it was), it's fairly easy for Chinese chefs to pick it up, the taste is the same no matter the ethnicity of the cook.
correction: SOME white taste buds. (again no intended racisms). a joke i often bring up in front my friends would be, white people's definition of "good chinese food"/chinese food that they know about, has never been anything other than lemon chicken, sweet and sour pork, chow mein, and chop suey. story goes on: what on earth is chop suey anyways? it took me YEARS to even find out what on earth that stuff is. it didn't sound like any dish that i know of neither even if i attempt to translate the name. since after all we've never heard of it in hk, so i had this "mystic quest" to find out what on earth it is.. through the internet. i wasn't even a bit amused when i find out it's not even some real chinese dish.
there's a sushi takeout done by vietnamese people at cambie and 41st in vancouver, and sometimes i go there merely to fill my stomach up(each piece is huge).(i won't go there if i want some serious food) one time i saw a white customer inside telling the shop staff that he thinks that place has the BEST sushi in the entire city and would recommend everyone there. i mean like, SERIOUSLY?
anyways...
with that said, so-called food experts labelled the century-old eggs as the grossest food ever. it made me wonder if they're the same people as those who said china still uses swarming tactics with ww2 weaponry..(don't know what they're talking about)
all these examples reminds me of those people who graffiti random "chinese" characters and ended up having something on their body that either doesn't make sense or completely embarrassing. to us it's funny because their lack of understanding of the other culture had created comical incidence.