Hey now, watch what you say about Italians!!
(Yes I know us Italians have a reputation for being very emotional people!)
I remember when my father passed away, and this is really sad but one of the first things that popped into my head was "OMG I am going to miss my concert in a few days!" And I was so mad at myself for thinking that because, hello my father just died. I didn't even really give a darn about the concert.
My point is, that when someone close to you dies, sometimes your mind is just trying to make sense of it all and it makes no sense at all. So you might say or think odd things. Its just a very surreal feeling. Not only that but one minute your crying your eyes out the next your remembering wonderful moments you had with that person.
John not only just passing but being murdered was probably one of the hardest thing that Paul had ever had to go through, and he was just dealing with it the best he knew how. I am positive that he was just so overwhelmed with every kind of emotion.