Ph.A.Q.: How does someone know how much gold I have?

Today marks the first of the Ph.A.Q.'s a series dedicated to answering users questions.  If you'd like to learn more about how your question can be featured, check out my page about it here, and get your question in ASAP!  

So here's this week's scenario, sent in by Curtis:

"I had something wired happen to me the other day, wondering if you have ever heard of it or know how they did it? I was on my alt bank/guild toon the other day when this guy started asking me for money cause he was from a different realm and didnt have any. I was friendly and all but refused to give him any. After a few minutes he asked again and I said I didn't have gold but lots of silver and copper. Seconds later he said no that I have 65,765 amount of gold, and that I was doing pretty good. The weird part is that he was off by like 5 golds and a few silvers of what I actually had ! I don't share account info with anyone but my son who was there beside me when it happened and I use a authenticator. Was this just a extremely lucky guess or is there a way he could have looked up how much I had?"'