Is it weird that my boyfriend's teenage son sits in his lap?

My boyfriend has 3 kids. One is 19 and in college. One would have been 17 but she passed away from suicide 3 years ago and his youngest is 14 almost 15. He has told me that his son and his sister when she was alive had intense trauma. His son woke up and came downstairs while we were watching a movie and my boyfriend asked was he okay and he just sat in his dad's lap and laid on him and my boyfriend just let him. I don't have kids if my own but should s teenager be sitting in a parents lap? Is that normal? My family was very hands off so maybe I just don't get it.