Show no weakness

We had a family snowball fight at the park tonight.  Poor Ezra got cold and actually became rather emotional so we took him home to put him in a warm bath (for those of you who know Ezra well, he's always smiling and chipper--seriously).  Before going in the bath he was laughing hysterically but it wasn't because he was happy... he was trying so hard not to cry.  He did this until he just broke down and wept.  We just snuggled and when I asked why he was crying/sad, he just looked clueless and said "I don't know" and went back to crying.
I know this seems pretty normal to most people, but there is something different.  When Ezra doesn't get something he thinks he should have, it's pretty noticeable when he's upset--not because he has a tantrum or cries though.  He will just nonchalantly walk into another room.  When I call him to come to me, he quickly wipes his arm across his eyes, turns around had puts a big smile on his face.  I can still see some of the tears on his face.  When I ask him what's wrong, he smiles even bigger and says "I not sad, I happy"--and by that time the smile looks quite unnatural.  He keeps doing this until I tell him why I think he's upset and that's when he can't hold it in any longer.  The forehead puckers, the tears well up and he can no longer keep the 'happy' façade.   That's NOT normal. 
We keep trying to tell him how it's okay to be sad and cry (goodness knows, the child has seen his mother cry a number of times).
Don't get me wrong, I certainly don't want a whiny, cranky kid, but every kid needs to be able to break down and be sad/upset/weak so that his mom & dad can help sooth and carry his burdens--he's 4 years old!
I love my boys and it breaks my heart to even think that one of them doesn't think that he can be vulnerable in front of us.