Plz tell me I'm not a terrible friend and did the right thing

I made friends with this mom through a Facebook group. We started talking and became really close. She had two kids. A 5 year old girl and a 16 year old boy. She has said her 16 year old son had a lot of severe mental issues. My dad suffered from mental illness so I understand. Every time we hung out I noticed she never brought her son, just her daughter. I thought that maybe he just doesn't like to come outside. I go over her house to pick her up because we were going to the park. She was running behind so I came in to help her. I saw her daughter and asked was her son home since I hadn't met him yet. She just said he's in his room. Her daughter blurts out "He isn't allowed to come out of his room!" And my friend tells her year old to shut the hell up. What she said and how my friend reacted I found weird but I let it go. So we go out and she goes to get some food inside McDonald's because the drive through is too long. I'm sitting in the car with her daughter and my 3 year old is sleeping and I ask if her and her brother get along. She said "Idk. He can't come out of his room." I asked why and she said "Because daddy will hit him if he does." I know I shouldn't be prying answers from a 5 year old but I was starting to feel scared for that boy. I asked if her mom does anything. She said "No. She says I'm good and he's bad. " I asked her does daddy hit him a lot. She says "When he comes out of his room." I just sat there in silence. After our little outing, I told my friend she should bring her son next time so we can all have fun. She got awkward and said "No. I think he's fine where he is." After I got home I called my mom to figure out what I should do and she said call cps. I spent a whole day debating and finally called cps. I feel so terrible and like the worst friend in the world. I just can't stomach the thought if a child who is already mentally ill being abused. Did I do the right thing? Am I horrible?