Does this mean bad as in moldy, bad as in not tasty, or both?
And if the food is evil, is this how you say it?
For 'moldy' we would rather use a more specific word ("spleśniałe", probably).
Most probable interpretation is "not tasty" ("niesmaczne"), although actually "evil" also works.
How strongly worded is this? Is this "the food doesn't taste too great" or is it "the food is disgusting and inedible"?
"really bad", I guess.
But frankly, I personally wouldn't consider this sentence to be a very natural one. "kiepskie" ('rather bad') seems more probable, or "niesmaczne" ('untasty'). And then some stronger words like "fatalne" (reaaaaaaally bad), "obrzydliwe" (disgusting) and "niejadalne" (inedible).