Actually I can tell you from my own experience that it's easy to sometimes get lyrics more messed up with a sheet of lyrics(or in their case a monitor) in front of you.
You have your eyes closed, your feeling the music, then you open your eyes right before the next verse and your eyes go directly to the wrong verse. Your brain has a synaptical collapse and you mumble something into the mic as you attempt to get orientated to the right verse.
I don't blame Paul at all for this happening in his
first real gig with the band in front of a worldwide audience. You think you could do any better? He's only fucking human.
I think Paul is doing a great job considering the task at hand.