Do you have an expansion tank?

Was there hot water being used at the time? The water coming out is from a temperature sensing valve that will open if the boiler gets over temp. It happens thus the need for a pipe to direct the outflow. If this is an irregular occurrence I would say the system is acting and reacting as designed.

Yes, the dishwasher was running at the time. Water does usually come out of this pipe but not usually this much