**解释：**

He was blown because he was born as a prodigy of playing the clarinet.

In this idiom, "号手出身" means being born or having a background as a trumpet player. The word "号手" refers to a trumpeter or someone who plays the trumpet. The phrase "出身" means being born or having a background in a particular field.

The second part of the idiom, "为什么是会吹", literally translates to "why he can blow (the trumpet)". In this context, "吹" means to play a wind instrument, such as the clarinet.

So, the idiom "号手出身为什么是会吹" is used to describe someone who is naturally talented or skilled at playing the clarinet. It implies that their ability to play the instrument is innate and effortless, as if they were born with this talent.

As a literary scholar and website editor, I find idioms like this fascinating because they convey cultural nuances and playfulness in language. They offer creative expressions that add depth and color to our communication. By understanding and using idioms appropriately, we can better appreciate the richness of a language and its cultural heritage.