Defeating 1600 rated chess computer on chess.com I just defeated a 1601 rated computer in under 3 minutes. Normally, it is a lot more difficult to defeat players having rating even 1500+. 

I want to understand how is that possible. Was it a computer that was wrongly rated at 1600+ or did I really outperform it? 

[FEN "7k/8/6p1/8/7P/8/3r4/4q2K w - - 0 1"]


It never looked like a computer playing at 1600! What really could have happened?
I want to understand, how is that possible - was it a computer that
  was wrongly rated at 1600+? or did I just outperform it really?


Neither.

You don't understand rating systems. There is no absolute rating system in which to say the computer was or wasn't playing at 1600 strength. All rating systems are relative. They measure the relative performance of the players results in that system. There is no judgement of the quality of the moves.

If the computer rating system is accurate then if you set the computer program to play against the same computer program (with you feeding in the alternate moves) on another computer and one is set to play like 1600 and the other like 1700 then over a large number of games the 1700 computer should score a certain percentage against the 1600 computer.