Actually the "default value" in the link mainly tells on the default value of the DATETIME datatype and the date value is not beyond that.

The usage of the GetDate() as the DEFAULT value (which is has a constraint) it always picks the today's date and time and it never pick 1900 one.

Because, (like the other said) "single space" or any non string in the non-date format will always returns the default value (and not because the DEFAULT constraint, but because of the datetime datatype is the way it is)

try the below code, it takes exactly the today's date and it inserts.

insert into #test (id, empname) values (4, 'qtod')

When a value is going to be passed to the column which has DEFAULT value constraint

1. either you have to pass perfect value of the date which can be the date other than 1900 one

OR

2. do not pass the value at all to that column, and let the constraint take care of.

passing single space and zero (not sure, and which I have not used anywhere in real projects) does not adds the meaning to it.