Water began flowing from some taps even with whole house shut off
Okay, we gained more info in the comments, and now the order of events seems clear:


You turned off the water to the whole house,
opened taps on the first floor AND second floor to drain the pipes
closed taps on the first floor and then went to work
after about an hour, the taps on the second floor start to drip


We can now see the reason for the delay: Clearly the 'whole house shutoff' was not completely closed, and the water had to slowly fill all the pipes up to the level of the second floor.  If you had left a tap open on the first floor, you would have seen the drip almost immediately.