I agree with naive rather than stupid. It's not like Zaha signing a long new contract which basically sealed his fate. You have to remember that in 2018 when he signed his new contract Spurs finished 3rd, having finished 2nd the season before and seemed to be building stuff. Quite literally as well in terms of their stadium. Following year they got to the Champions League final so the new deal seemed to make sense at that point. Then the wheels completely fell off, Pochettino was sacked and Mourinho continued the slide.
I think in 2018 he genuinely will have thought he could win stuff with Spurs. But that Spurs team is a long way off from the team they are today.