I was under the impression that most low times were -mistakenly- so, due to lagging through walls/the timer not working properly.
Not true at all. There are times on those leaderboards that are humanly impossible even with the ability to walk through walls. The only time the timer goofs is the rare 0.00 timer glitch which was patched out forever ago... well before the leaderboards got beyond saturated with 0.00 times.
These people are blatantly cheating. And I really don't get it either. Why would you buy a game you don't intend on playing just to get steam achievements? I mean seriously, don't you have something better to do with your time and money?
Some people literally don't.
I was number 1 on the Limbo leaderboards for the 360 last summer, and as they were based on finding all the secrets and were static (once you did everything, your position could not be beaten) my group locked up the top 10.
Then hackers started appearing with impossible completion percentages and spamming boards with how to guides that were completely invented just to waste people's times. It got to the stage where the developers made an official statement regarding the real percentage and gave all the legit top 10 a prize, which was really good of them, but this still didn't stop the hackers spamming forums and sending abusive PMs for weeks.
I find it almost impossible to understand what motivates them other than spite towards people who can do things they can't, no matter how meaningless, so they have to fake their own achievements and then try to discredit those of others, even when they're dealing with complete and utter strangers.
It's a form of psychotic insecurity and what's worrying is if they're willing to do it for a game, imagine what they're like secretly in real life when it comes to things that actually matter.
What did you get?

I have glitched once or twice usually to just unlock a DW or on Ch 6
y i got a 3 sec time on level 1 in ch 6(?) and only landed 45th. that's just sad