Terry was working at the computer when Myst came up to her with a "Meow! Meow!" to command her to follow him. She was a bit slow to respond, but eventually she got up to follow him.
He lead her down the hall and into the room where Richard was working on his computer. He sat by Richard's chair and said "Meow! Meow!" Suddenly, Terry realized what had happened. Myst had been sleeping in that chair for the past few days and he wanted it emptied so he could sleep there again.
In other words, he wanted Terry to get Richard to leave, so he could have his bed back. I think that is justified. I do not know why Richard would want to use Myst's sleeping spot anyway. And I REALLY do not understand why our pet humans were laughing so much over this.