Hamlet and the Gravedigger

When Hamlet and Horatio first see the gravedigger, Hamlet talks about how the skulls the gravedigger is throwing up could have been wordy politicians or suck-up nobles, and how now, they are being tossed around with a shovel. The message that he sends is that death makes all equal.

But when the two speak with the gravedigger, who plays with their words, Hamlet quips, "...By the Lord, Horatio, this three years I have took note of it: the age has grown so picked that the toe of the peasant comes so near the heel of the courtier, he galls his kibe."

I was rather confused by what Hamlet meant, so I went to No Fear, which says, "...Lord Horatio, I've been noticing this for a few year now. The peasants have become so clever and witty they are nipping at the heels of the noblemen."

Hamlet is looking down at the gravedigger, and marking the difference in their ranks, and his lines sound like he is amused that the gravedigger should speak so boldly. This air of supremacy is not what I received from Hamlet a few lines ago, when he was pondering about death and how all men are equal in it.

Why the sudden change between philosophical Hamlet who is poking fun at the self-assumed airs of royalty of nobles, to a Hamlet, amused that a peasant should talk back to him? Could he be threatened by the fact that there is less and less difference between the classes?