SPOILER (kind of ?)
I feel like Sentinel was a second father to Chad during those 10 years he can't seem to remember. After what happend when Chad and Fred got searated, maybe Sentinel took care of Chad for some time ? He's definitely connected to Chad since he seems to know him.
The last scene got me the impression that Terry (Chad's dad) was beating him...... I may be wrong but i could see some sings that maybe it was the case... If Chad has PTSD when he sees a metal bar on an empty hand then that's a solid clue for me. Along with Terry's demeanor during the flash back.
Anyway, lots of mysteries and unanswered questions, i loved this update and am looking foward for the next one !