Pietro looks toward his sister when she reaches for his hand, and instinctively clasps her hand in response to the touch.

"We're meant to socialize with one another. I think." Which could be awkward depending on whether or not we want to pretend that Age of Ultron ended differently. Either way, Pietro has no real desire to go out of his way to interact with others. His sister is here with him now, and that is all that he needs.