flow, boil
滾 centers on turbulent liquid motion: water flowing vigorously or boiling up. The two given meanings are different intensities of the same churning movement.
滾 combines 氵 (water) with 袞, which likely contributes the sound コン and the idea of rolling or churning. The exact historical development of 袞 is uncertain, but the water radical clearly ties the character to liquid motion.
Water 氵 on the left and a complex right side that looks like a container with something bubbling inside. Picture a pot of water boiling over a fire, the surface churning and flowing.
For コン, imagine a con artist stirring a boiling pot of water to create a distracting flow: con -> コン, and the water churns.