It was an unexplainable feeling, but the best way for Adam to describe it, was that he could feel large amounts of energy in one place, along with lots of it being used.
Energy couldn't be created or destroyed and after being absorbed and stored within the body, could be unleashed through many different ways and that energy would return to the atmosphere.
After returning to the atmosphere, it would spread around in different forms, but the large use of and collisions of energy was very alerting for a cultivator, especially one with sharp senses.
Adam had suppressed his senses from reaching outside of the mountains that he had stayed in with his master, however now that he had left seclusion, he had spread them as far as they could go.
However, that wasn't necessary to be able to sense the commotion that was occurring as it was so large that any average cultivator would be able to sense it and gauge what direction it was coming from.