IP addresses are four numbers (or six) separated by dots, usually read as 'point'. The maximum value of any one number is (2^8)-1 or 255. The number given is 4.77.518..(obscured). No IP address can have 518 in it.
IP addresses aren't registered to any names at the global level, so the plot device of simply identifying David Cho by the IP address fails. However, it is possible to identify a computer using an IP address, and then to identify the primary user of the computer. This is more complicated than shown, but is possible.