Flight Instructor reported witnessing an NMAC of two aircraft in landing phase.

Narrative

I am a CFI-I out of the flight school located at ZZZ airport. I was not in the aircraft at the time of the near miss; but I witnessed it on the ground at the airfield. Two aircraft were coming in for landing (Aircraft X on Runway XX; Aircraft Y for Runway XY); Aircraft X was making position reports coming in to land on left traffic Runway XX; while Aircraft Y was making zero radio calls; directly coming in on a final Runway XY. Aircraft Y came in first and landed; while Aircraft X came in second on the crossing runway. They landed and appeared to get about 30-40ft within one another. After landing; Aircraft Y came on frequency and said 'sorry wrong frequency' and then proceeded to depart the airfield after taxiing back to Runway XY. After reviewing track logs of Aircraft Y; it appears they do this quite often at almost every airfield they do land at.To prevent the situation; the pilot of Aircraft Y should receive corrective action and fly with a CFI to relearn how to enter controlled/uncontrolled airfields; along with traffic pattern operations and radio communication/phraseology. Additionally; if the pilot doesn't hear anyone on frequency; they probably should double check their radios before they enter an airfield.