With reference to IEEE 1800-2012 Section-18.5.10,
Variables can be solved in an order that is not consistent with the ordering constraints, provided that the outcome is the same.
Here, 'x==0' is solved first since it leaves only single value of 'x' and it is not dependent on any other statement. Then 'x>y' is solved and 'y' is solved with some negative value.
Even though the last statement 'solve y before x' contradicts the actual solving order, none of the other variable solving statement has been contradicted. The final outcome is same even if 'y' was solved first. Hence, the last statement is of not significant over here.