Engine seize?

I was driving my 2007 Subaru Outback yesterday when I noticed my brake, AWD, AT Oil Temp, Oil Pressure, Battery, and Check Engine light turn on. Immediately after, the engine shut off, the power steering was disabled and I coasted to a stop. I have not been able to start up the engine since. I did not notice any rattling or grinding sound as the engine cut out.

I thought maybe my engine seized because of low oil. Now I am second guessing that because I filled up 3 quarts of oil and now it is over the max limit. When I have tried to restart the engine, I just hear a buzzing sound and I can see that the drive belt is still turning. There does not seem to be any battery issue, as all the electronics are still functional.

My major question here is whether or not you would think my engine is seized. If not, any guesses as to what might be the issue? Thanks!

Just because you have lights doesn't mean your battery is good. Measure voltage static and measure while you try to crank.
How old is your battery.

I have not replaced the battery since I purchased the car over 2 years ago. I have never had any battery issues before but could a bad battery cause the engine to cut out while driving?

I have not replaced the battery since I purchased the car over 2 years ago. I have never had any battery issues before but could a bad battery cause the engine to cut out while driving?
Yes. Get your battery load tested and your charging system checked.