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А чем это отличается от того, что делаю я?
{vs}: А как это отличается от того, что делаю я?
Although I'm aware that "чем" is the right word to use to express the idea of "How is it different from ...?", I can't quite put my finger on why "как" sounds strange here.
Отличается requires a noun in instrumental case when you are talking about what is different. Hence чем.
Этот банк отличается надежностью - The bank is known for its sustainability.
On the other hand, как in this context will mean you want to know to what extent one thing is different from another (Как is a question to be answered with an adverb)
Как отличаются эти графики? - How big is the difference between these curves? Очень сильно - Quite big.
There's a formal semantical difference, which @AlexVB correctly pointed out -- "difference in what (aspect)" vs. "difference by what (measure)".
And there's a usage difference. I think you'll find the second variant isn't actually used (maybe that's why it sounds strange to you). If you'd want to ask "by what measure this differs from that", you'd want to say, e.g., "насколько (это отличается... и т.д.)".
