Why would he do this?

My sons father had my son Saturday at 10 am to Today (monday) 12:45 pm - anyways my son came home with a large bruise on his lip and a bruise on his ribs and was complaining about shoulder pain. He told me that he fell playing basketball and that his uncles (that are just two years older than him) pulled him while he was laying on the floor. Anyways I text his dad about his shoulder asking what happened and he said "What?" and then I said "He has been complaining about his shoulder since he got home and has bruises all over" His dad said that "He played ball and with the boys all weekend so I don't know, he didn't say anything to me about it"

Anyways about 3 hours after he got home the police showed up at my door inquiring about child abuse on my son. His dad called. I was shocked t say the least and they questioned him and determined it was unfounded. So essentially did his dad call the police and claim that he abused him? Does anyone really understand this? I made no inclination of abuse - just asked what happened in case he may have been injured. I am so lost on this one....