"How" type thinking and "Why" type thinking

There was an interesting scene during some training the other day with system engineers who build applications.
We threw a question at them.
The customer came to you and said "I want a new popup message in the system, can you do that?", how would you respond to this customer?
All system engineers who were there in the class answered "What kind of popup message do you want?".

This was pretty surprising and shocking to me. The first thing that popped up in my head was "Why do you want a new popup message? What for?". But they were rather focused on how they can build it into the system.

My question is, how can you build a system without knowing the background of the customer's request?
This might be one of the characteristics of the way people try to solve situations. In this case, putting the interest on the system side where they are a professional at. But the key to reach the goal is to understand the customer and keep asking "why?".