Probably a skilled player, possibly under an alt to that makes you suspicious. (Encountering someone "new" can usually lead you to be sceptical over someone you've seen for a long time.)
Regardless, there are no 100% sure fire ways to tell if someone is using an autoblock through visuals, I mean, your enemy could just have been good as I say.
Let the machines with their coding recognise it, trust in chadz & co. Never accuse someone of autoblocking either! ;)