I can't exactly say that "how" they noticed that but basically, admins/devs can see your IP address, device and stuffs. So, they noticed that two or more accounts are being used simultaneously from the same IP and probably, the same device.
By earning 150 xper, you will reach Xper Level 2 and then you can post 5 questions and 2 takes every 24 hours. :)
because people do that shit and give themselves MHO to boost their stats and Xper and stuff. Ofcourse they are gonna crack down on that, you're essentially stealing money from them when you think about it haha.
Both of your accounts would have had the same I. P address.