The gray numbers displaying as 664 is not a feature, nor a bug. Its just a placeholder. In version 0.0.2 (which I currently have on my phone but is not yet uploaded) the gray numbers the input box shows is current comic number that you are on.
As for showing a random comic, that would be very easy to implement. However, finding a place for the button display to go won't be so easy. I'll try to submit 0.0.2 by the end of the day, with the random comic feature included.