Interacting with a child who has been abused in the past?

[Hope]

I'm talking about my cousin Ryan. He's ten years old (almost) eleven and I recently saw him over xmas break in Chicago. He's an adorable kid. You know, blonde-brown hair, olive skin, brown eyes. Just really cute. And because he's so cute I will occasionally poke him in the side to make him laugh or give him a little tummy tickle. His mom will sometimes tickle his stomach briefly as he's walking by and he doesn't seem to mind at all. He is excruciatingly ticklish. But, over xmas break, things got a little more intense. On a few occasions, I held him down and tickled him mercilessly on his stomach, sides, ribs, neck, etc and got a great reaction. Which made me wonder if maybe his feet were ticklish...so I ripped off his socks and started tickling....I apparently found THE SPOT because he started laughing hysterically and eventually screamed. I don't know if that partly has to do with the fact that he's never had his feet tickled before (they've never really been touched by anyone) and they're just not used to stimulation or if he's just REALLY ticklish. But none of that's important. For one, Ryan hasn't seen his dad since he was six. His dad was abusive to him and his mom and his mom left the dad after he broke a few of Ryan's ribs. I don't know how this has affected Ryan. He seems like a normal kid so maybe he's recovered idk. But, anyway, I felt bad later because it seems kind of messed up to hold down and tickle a kid who has already been through so much. Could it be traumatic for him to be tickled? Is it scary for him? does it bring back bad memories? He seemed ok afterwards but i just can't be sure. So....was that wrong of me or is it ok for me to keep tickling him during visits?