Now, come on, today’s writers can’t be expected to understand subject/verb agreement, can they?
What they don’t understand is the subjunctive.
Since they don’t understand it, they just look around, and if there is an “if” somewhere in the neighborhood, they say “were,” whether the subjunctive is correct or not.
The reason it’s not correct is that the statement is not contrary to fact. There WAS a popular cartoon character on the box!