They gathered machine information during beta signups to see who was running what, and I imagine they base any client decisions on the information they gathered during that time.
The information they gathered on "Mac" users would have been severely skewed. A very small minority have the time and money to Bootcamp their machines to play a single game. The amount of Bootcamped Beta testers would be a small number because of the added hurtles those users would have to go through.
Given that the signup required a Windows client most Mac users would choose not to bootcamp and thus not sign up. This also is not an indicator of the demand for that platform.
The logic that Bioware based Mac demand on the Beta testing weekend is inaccurate.