One of my sites had 80 people viewing the site at one time all the time yesterday. Just one after another all day long clicking into the site about 1 every second. Massive amounts of visitors for it to have at one time or for the day total. The interesting thing is they appear to have come from one country, google.pl, Poland. Now all of the sudden the traffic is gone the next day. The term that brought them in is a well ranked top 10 term already, so it doesn't seem like it was big change there. What could have caused the huge spike like that and for it now to be gone?
Possibility, a news story on that topic in Poland that day, and people searching for more background using keywords that you show well in. Without knowing what the search term was it is only a guess.
These things happen. I forget now what the page was, but for almost a full year I had excessive traffic to one particular article on my site and the referrer was some overseas site in a language I couldn't read. No idea what made it interesting, no idea why their site was popular for so long, but it dwindled away after a year. (shrug) it happens..