A different brand would require the appropriate licence to use for the survey. A fake IP, similar to a made up park, would be too contrasting and wouldn't lead to real measurable results.
The survey was most likely to confirm the preference of the IP at the park it was intended for. They had a hunch, but considering the cost involved of licencing the IP, they needed some form of research to back it up / get permission from the board.
Planning permission for Project Horizon was also submitted almost two years before the Branded Surveys survey, and two years before the announcement of Project Refresh and Play.