While it's less common now, as there's countless cars out there proving it's a load of old bollocks, you still see people commenting that they can't/won't/shouldn't/couldn't use a certain turbo because it's a "diesel" turbo, and their car is petrol.
But do "Diesel" turbos exist? Well, maybe back in the day, but in this day and age? No, not really. Turbos that are the wrong wheel/housing spec to suit a certain engine? Yes, 100%, but what fuel the original engine it was designed for is not the issue here.
Frankly almost all turbos, yes, even the most high-end aftermarket ones, have at least 'some' parts originating on a commercial diesel engine, and many, many, consist of parts that almost all OEM on some diesel engine of some description; they simply consist of choice parts of various diesels to make a good spec one for a typical tuned spark ignition engine.
In fact there's tons of OEM turbos that work straight out the box as fantastic performers on tuned petrol engines. A whole crapload of 'famous' BorgWarner S200/S300/S400 turbos people use on some of the worlds top tuned cars are also OEM on various things, in fact a lot of them John Deere (yes, farm machinery!) engines. Yep, awesome spec, even billet wheel, Borgs are fitted to tractors, combines, generators, and more.
And things like the 12cm Holset HX35 is hugely popular in the tuning world, and proven ridiculously capable on tuned petrol engines, despite being fitted to countless diesel 'things', even diggers. Much the same for the 10cm Holset HY35, which is mega popular on things like 1JZ engines in the UK, proven 520bhp+ and 500lbft+ despite hitting full boost under 3000rpm, but they're OEM fitment to various DAF engines among others.
OEM 'diesel' turbos may not be THE best turbos in existence, but the sometimes amazing performance combined with reliability and a low price often makes them THE most value for money.
The problem with 'some' diesel turbos being great for tuned engines is some people go to the polar opposite of the people who think diesel turbos are the car equivalent of Ebola, and instead think they can fit any old diesel turbo to their engine and expect it to perform well.
Fact is, as good as some are, most of them aren't suitable for performance petrol applications. Most have a FAR too big turbine side to work well on small capacity engines, so unless you know it will work, or actually understand turbo sizing and what turbo you're looking at, don't do it.
Obviously business is business, so big aftermarket turbo sellers will slate "Diesel" turbos 'til the cows come home, even going as far as to tell bare faced lies, as they don't want people to buy them instead of their own, even if many of theirs are barely changed over an OEM diesel unit.
Like it or not, the fact is, there's a LOT more money to be made in OEM than in tuning, which is a tiny % of the turbocharger world, and for that reason the top OEM engines get the best, most high-tech, turbos, long before the general aftermarket. Christ, even normal, low power, 4cyl Mercedes Sprinter vans now run twin compound turbochargers, both with billet compressor wheels. The only things they don't get vs the aftermarket are gimmicky or unreliable things- OEM is built to last... ;)
DON'T GET ME WRONG- The best turbos, the most powerful and fastest spooling turbos, are not OEM, they are aftermarket ones, but you will be paying the premium to get these, and only you can decide if that money is better spent elsewhere (Hint- Usually).
Honestly, aside from very very few, literally mega-bucks, Pro drag units, and of course things like proper WRC/Rallycross/LeMans race turbos like Garrett TR30Rs, they're all based on OEM "Diesel" units to some extent, be it just a turbine wheel and housing, or much more...