Update: it might not be the screen after all, but a cable that needs to be moved a bit.
This is mostly for google, because I tried a lot of software fixes, but in the end the ghost touches turned out to be a hardware problem.
I have a thinkpad x1 tablet (1st generation). All great, no sound / no fans, 3:2 ips screen, lightweight. Ideal for reading. But some weeks ago I suddenly got ghost touches. That is, there seemed to be some random touches, touches that were "stuck" even though no finger was on the screen. On top of that the edges of the screen did not react to either finger touch or styles/pen input. After fiddling around a lot with the settings in the os (win 10 mostly), I found no solution, and in the end ordered a replacement screen 1. Replacing the screen took quite a while, but the hardware maintenance manual was quite helpful. Now everything is fine again.
So yes, in the end it is a hardware issue.