Anyone who has done much meditation knows all too well that the brain is constantly spewing out random thought activity. That’s just what it does. How troublesome that is depends mostly on how you use attention.
That thought chatter is just one possible “channel” your attention can tune into. Sensory inputs are another (including your sense of your own body). Deliberate, disciplined thought is another. If your attention locks into the mind chatter, you feel swept along in this crazy tumble of images, fantasies and feelings. But you can exercise the executive control functions of your brain to focus your attention away from that chatter and onto one of the other channels. Meditators often do this by focusing in on the breath, but you can do much the same by opening up to your surroundings, or just getting in touch with your body.
Note that tuning into these other channels doesn’t mean that the chatter stops; it doesn’t. But it no longer becomes compelling or relevent, and isn’t perceived as a problem.