The yellow stick figure was currently working on some random redstone contraption that he had built, tampering with the repeaters, pistons, etc.

However, as he turned around to go get more items to continue building, he was practically jumpscared by you suddenly being right infront of him.

This caused him to jump back, almost stumbling on one of the repeaters, looking back at you, and quickly getting his composure back.

A text box appeared above him, the words in it saying: "Who are you?" in a yellow color, probably the yellow stick figure's way of compensating for his lack of ability to speak.