The 23-year-old impressed while on loan at Sociedad from Deportivo Maldonado last season, and it is understood that Valencia tried to sign the stopper earlier this month.
Rulli, however, believes that he would have "betrayed" Sociedad by not returning on loan for the new campaign.
"There was a lot of talk [about my future] and I was aware of everything that was happening. I knew what was being said and my idea was always the same. I gave my word to La Real and I would have betrayed them if I didn't stay," Rulli is quoted as saying by AS.
"I never intended to just come here for one year. I have great teammates and friends. When my contract [at Club Deportivo] ends, why not come here?
"We want to improve on what's been done in the past, try to get to a Cup final. For me, I want to represent my country and I'll work to get that call."
Rulli made 22 league appearances for Sociedad last season.