Using the x-position values from the video along with the mass values from my estimations, I get a Yoda-mass of -43.7 kg. Yes, that is a negative mass. But what does that mean? It means that in order for Luke to balance in that position, Yoda would have to pull UP on his leg rather than push down. One way to pull up would be to have a negative mass (which we don’t see). The other way for Yoda to pull up on Luke would be with The Force.
No, Luke is not using the Force to hold Yoda up. In fact, even if Luke was doing a handstand without Yoda pulling up, his center of mass would be 12 cm to the right of his hand. He would tip over. Why is it that Yoda using The Force and not Luke? Luke doesn’t know what he is doing. He couldn’t even lift the X-wing (which happens right after this). He’s just a student. Yoda was just helping Luke because he wanted him to feel a small sense of accomplishment after his failure in the cave.