Should I check up on my ex boyfriends 18 year old son

I was with a guy(some of you know my.story) who wss abusing his son. I always saw his son as disrespectful, but the amount of abuse he suffered... I understand. He smashed his sons laptop because his son asked us to quiet down so he could study. And when his son yelled something like "What the fuck!" When his dad did that my ex took his son, ripped his shirt and smashed his face into the wall over and over again and kicked him out for the night. He also beat his son and held a gun to his face because he didn't turn in 2 homework assignments (because he smashed his laptop). I had called the police on that psycho he pulled that gun to his sons face. His son was curled in a ball on the ground crying. My ex spent a night in jail. I've heard that his son still lives with him at that apartment and saw his son pop up on my recommended on Facebook.... Would it be wrong or weird to check up on him?

Edit: He was 18 when I met him. Me and his dad weren't together super long. He could possibly be 19 now but he was already 18 when I got with his dad. He's had other girlfriends and wives before me who also knew he beats his son. He never beat any of his girlfriends or wives though. Just his son.