3 Mar 2014 - How to spell "up"?

Today while I was on my way home with Javier, he suddenly asked me a question........

Javier:"Papa, do you know how to spell "up"?"
Me:"I know.....do you know?"
Javier:"I know!"
Me:"Then spell it."
Javier:"It's U...P...P..."
Me:"No it's wrong!"
Javier:"Yes it's correct!"
Me:"No it's really wrong. Who taught you that!"
Javier:"It's correct!"  He then pointed at the road sign in front of our car and said......
Javier:"You see the arrow is pointing up, so it's "Upp"!!!!!!"
Me:"..........."
I was speechless and had no idea how to explain to him at that moment........