He could have been a grandpa checking it out? You never know what people are doing, my DH was just laughing the other day because he was meeting his dad (DD and DS's grandfather) who is very involved with our kids at a playground. DH was running a bit late so grandpa was waiting by himself in the playground. It was cold so he was wearing a big coat and hat. DH commented what a weird old man he looked sitting in a playground all by himself.
I guess my point is that sometimes people do have innocent motivations, they just manage to look a but weird going about it.