We see this phenomenon on phones occasionally. It's popularly referred to as "ghost touch" and is a result of damage to the digitizer that allows electrical noise on the signal lines that gets picked up by the processor and interpreted as touch inputs.
Unfortunately this is a hardware problem and the only solution is to replace the digitizer. On phones that means a complete screen replacement, but that may or may not be the case on your eReader. Some tablets do come with separate components for the display and the touch screen, while on others they're fused as a single unit.
A big problem here is that according to Kobo, the Libra 2 isn't designed as a repairable device like the Libra Color, although it's not clear to me exactly what all the differences between the two are. It appears from the Libra Color guide that the display and digitizer come as a single unit, so my guess would be that yours probably is too, but I wasn't able to locate a replacement guide so I can't confirm that. Likewise I had no luck finding replacement parts for it either; I'm guessing the e-ink display hasn't made it into the mainstream aftermarket industry.