In a 2007 Toyota Camry why would the maintenance required light come on if it doesn't need an oil change? What else could it mean?

The 'maintenance required' system counts miles, and it also counts engine revolutions and running time.. So if you idle a lot, and/or drive in a lot of traffic at low speed, it will trigger it sooner than 5,000. So it really is time for an oil change. If you are using synthetic oil, write down the mileage or put one of your "Trip" odometers to 0 and go another 3000, (recommended) no more than another 5,000 (total 10k) Just re-set it using the instructions in Tom's link.

The only thing they left out in those instructions is have your odometer on total mileage, not trip A or B when you do this. Sometimes, and only sometimes, it won't work with odo on a Trip setting