I think he means GUI, and no, if you say array size is 1, it is really 1, but never set it to anything but 0, because it is fully useless.
What it does in the background is it tries to initialize every index from 0 to (the number - 1), so if I have Trigger array variable which says "Initial size: 10" it will create 10 triggers at indexes 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.
However this is not really good, because if you make few arrays that need to be constructed of size 8191(maximum), your map will fail to run initialization triggers properly, because you will hit "OP limit"(thats how we call it) before finishing initializing the variables.
Arrays in Jass are always of size 8191(indexes from 0 to 8190) and can not be made bigger or smaller. vJass does the same thing, but forces you to not use higher indexes(not true inside structs, which basically cuts the array into 8190/array_size pieces)