Theres no way to tell if its Leicester fans no, but the admins of a website have access to a great deal more info about you than just an IP address, ever wondered how those dodgy porn sites know you want to meet hot girlies from Leicester?, in exactly the same way that the club will be able to filter out anything that doesn't originate from Leicester.
Whether your on cable, BT, Talk,Talk Sky, or whoever, the bit of equipment that your modem connects to in the exchange has an IP address and a name which in most cases will include Leicester or an abbreviation of. The lists of these are freely available so all the club has to do is filter out anything that comes from anywhere else and while they'll filter out some legit fans they'll also filter out the sheep, trees and scum that want to sabotage it all.
Anyone that wants to see part of that info for themselves open up a command (DOS) prompt and type in tracert
www.bbc.co.uk hit the enter key and wait for it to do its stuff. Depending on whether you've got a router at home the 2nd or 3rd line onwards will start to contain the info that identifies the exchange your connecting to.
Many of these location finding sites don't bother looking for that info they just look at the IP address and as those can be duplicated across the country frequently get it wrong.