I'm assuming you didn't buy the pre-paid maintenance plan? Most likely the "free" oil change was to get you back in to the dealer, and then they would hit you up on the other 'recommended' tasks - tire rotation and fluid top off.
My (ex

)dealer offered an "auto for life" program where they would cover the drivetrain for as long as you own the vehicle - so long as you have EVERY BIT OF REPAIR AND SERVICE PERFORMED BY THEM. Not a bad deal if they were a "customer service" oriented type of dealership. But, just have one oil change done somewhere else - for whatever reason - (even under the toyota PPM plan) the deals off.
From my findings, the pre-paid plan gives you the general service every 5K like oil, filter, fluids, tire rotation, inspection stuff. I was told though it does not cover the other "recommended" items (such as fuel injection cleaning, etc) that is recommended - but not part of the plan.
Hope this helps.