Have you updated ESX recently? Did you have the tools set to automatically update?
No updates of late(not in several months). Even automatic would not do it upon opening the console one would think....It's puzzling. It doesn't do it again, after the first time, but it's definately strange.
i have seen something like this to when you update or softreboot a vm it doesn't reboot then when you open the console and move your mouse over the screen its going to reboot.
ik have disabled al screensavers in my windows vm's