I think your friend gave you a "wise" answer.
You asked him a silly question, so he gave you a silly answer.
But if he was serious, then you two are in serious trouble with Math.
x+y = ???
That is all the information?
8th Grade or not, that cannot have a unique (only one) answer.
No. If a variable is unknown, 1 cannot be substituted for the variable just like that. For that matter, any number cannot be substituted for the variable just like that.
You have to have a reason to substitute any number to a variable.
Could it be that your question to your friend is not complete yet? Could it be that there is additional information that would say or imply that certain numbers could be substituted for x and y?