Is this evil or genius? Faking Job Offers to get new registrations

A couple of days ago I've received a very juicy ($$$) job offer from a company which prefer not to say its name. The company has a product for developers. In one part of the form to apply was this question:

"What would you do to X(their product) to improve its design?"

Lets analyze this question:

1. It force you to create an account with them to properly answer the question. Those new "registrations" can be shown to their investors as proof of interest.
2. They receive honest feedback for free from their target audience.

The next day they wrote me to tell me that they won't continue the process with me.

The quick discard let me thinking. Was I used? Was this a dirty trick?