that's how a piano is like a drum.为什么用how

当你使用Why的时候,说明有既定事实,不要套用中文的意思（或者部分套用直译的意思）——
Why is a piano like a drum? ------ means somehow a piano is like a drum. (Which I believe, just don't know the reason)
How is a piano like a drum? ------ means there is no fact shows that , and I don't believe it.

应该有前后文吧 只有这一句无法解释呀 也许说的是二者间的作用或构造 用how应该可以