Why did the bottom water heater element fail before the top when run empty?
You should be looking at around 13 ohms for a standard 4500 watt heating element. If an element is burned up, your meter would have 0 deflection.
Our water heaters here in Florida always have the top element going on first because that's the first water leaving the tank and getting into your shower. Once the top thermostat reaches its setting it turns off and turns on the lower element. which stays on until it gets up to its setting. The bottom element will cycle on and off during normal hot water usage but when a lot of water is being used, the top one will start to operate to keep hot water leaving the tank. I have LEDs  hooked up to each element so I'm sure how they work.
My guess  is that you blew the top element because it would go on first but any combination could occur depending on which one was on at the time the draining took place.