My guess is that it’s an offshoot of the Scunthorpe Problem. My theory (without hard evidence) is that Bing/DDG have a blacklist of terms to completely filter out from results, but a whitelist of words that contain those terms which are exceptions to the filter. This would explain why “torpedo” is ok but less common terms like “Sharpedo” wouldn’t be flagged as ok. You’d have to find other examples with other blocked words to test this idea.