I've no doubt they can see if two keys are pressed in an instant.
I think people around here tend to misjudge how much anyone cares if two keys are pressed in an instant. The game is only going to do so many things at once.

When people say 1 key = 1 action, it's probably intentionally ambiguous so that hopefully people don't go too overboard, but what they really mean by this is that you can't set up a sequence that performs multiple actions including having to wait for the first one to complete. For example, pressing 1 and 2 at the same time nobody's going to give two shits, but if you press a key and it presses 1, and then a second later it presses 2 for you, then this is a problem. If you press a button and your guy moves around in a predefined pattern, hell maybe it circle strafes for you, and fires off abilities as you stand back and watch, then this is a problem. People make it out to be more complicated than it is.

They COULD see if two keys are pressed in an instant, if they wanted to put in a detection for that sort of thing, but .. have you ever played a game? Like actually played the game. How often do you press 2 buttons? A lot, right? So if I'm a game publisher, how do I make sure that my "multiple key press detection" isn't going to catch you physically pressing two keys? And why do I really care? Why am I going to spend time implementing this detection that -- as someone who makes games for people to play -- I know is going to have a massive false positive ratio because pressing two keys is natural? How much time do you think they want to spend implementing methods of detecting multiboxing, which isn't prohibited? And custom keyboards and mice, which a huge population of gamers uses and are also not prohibited? Hint: None.

I just read your guide and putting a 12 second timer in to a macro.. that looks a bit naughty ^^
Timers in ISBoxer don't send input after 12 seconds (there's no way to do that), they would instead stop something from happening when you're pressing buttons for a number of seconds and then allow it the next time you press a button after the time expires. Nothing naughty about it...