Is yawning just psychological?

It was a great day. I walked into a building and entered the elevator for the 2nd floor. This lady was already onboard and as the elevator door closed, she yawned. I asked her. “did you just yawn?” “Yes”, she said. I thought, well there goes the rest of my good day. Sure enough, after departing the elevator, I had my first yawn and it continued for the rest of the day. Question: is a yawn to humans, triggered by another person just psychological or is there something more?