The scowl is an interesting emotion, though Beverly doesn't bring attention to it just yet. Likely, it's a reaction of some sort to whatever she said, something in Sam's past that might not be the best to address yet.

"He's still relatively young, so he's still learning about humans and humanoid species, especially all of our slang. Understanding our meaning hasn't always come naturally to him, but it's been very rewarding to watch him learn. That's part of why he's got the emotion chip."

The other part is that his creator finally made something that worked and Data finally accepted how and why he got it. The chip functions as a way to make him more human and it's another step towards his life goal.