OK ..so I went through the demo and found that this guy joins at tick 143000. He is using aim assist and walls, As soon as you realize it you say "Okayyyy, I have a feeling he's hacking". He then turns his aims off and continues to wall. I know you realized at the time that it was a mistake..but I REALLY hope you learned from it. It's easier now because we can go back and look at sourceTV, however you never want a hacker to know you suspect them.
Moral of the story, yes..hacks.
Addition: Major obvious is at tick 142000 when he goes from his spawn around to t and back to double doors. Anyway..yup.