Meaning of "A voltage source “likes” an open-circuit load"
A voltage source shorted causes current to rise until something overheats or burns out. Therefore shorts are bad for a voltage source and could damage it.

An open circuit for a current source causes the voltage to rise until current flows. Usually the source will reach it's limit and stop regulating current. 

Both of those conditions cause the respective sources to stop functioning correctly. Hence they "hate" it. The opposite condition represents no load, hence they "like" not having to work.