I'm going to make an assumption, I see you have VIP, which is probably for a program. If you used the program on the same account as you're talking about now, it's possible to get logged out. Also; I have been logged out randomly without using any programs etc as well. It happens, just Neo things.
It's hard to say if it was random, or somebody logging into your account.
Besides pin, I also have b-day verification, and I change my password/pin at least 1 time a week, if you're afraid of being targeted.
But, as with everything in life, anything can happen, no matter what things you do.