2400MHz RAM is the speed that the RAM is rated and capable of handling without voiding warranty. Maybe you could run it at 3000MHz without any problems, but off the assembly line it's stamped at 2400 and the warranty will cover it to those speeds. Anything higher is at your own risk. Some companies will have a demand for 2400 and stamp all the RAM 2400 even though the day before they stamped the same chips to 3000. It's whatever the manufacturer garantees the RAM can handle using their testing and labling procedures.
The motherboard sets the speed of the RAM not the RAM itself. The RAM ratings are only garanteed not to blow up at these speeds. So yes your ram will run at 2133 no problems, just not garanteed to run higher than 2400 without problems, although possibly it could. That would be called overclocking the RAM.