> they do a referendum anyway, (90% win for getting out)
they do an illegal referendum so that 90% means nothing when many people didn't vote (obviously you are going to take a favorable result when only the people interested on it vote)
For more than 50% of the population to oppose secession, you'd need a voting turnout of ~90%, and for all the people who had not previously voted before to vote against secession. (50% turnout with 90% for secession -> 45% of voting population voting for secession)
If you get 100% turnout, and no one who voted in the referendum changes their vote, you'd need 91% of the new voters to vote to remain a part of Spain. Is it truly that implausible that some of the "leave" voters would have stayed away from an illegal referendum too?
Assuming that the results of the illegal referendum were accurate of course.
they do an illegal referendum so that 90% means nothing when many people didn't vote (obviously you are going to take a favorable result when only the people interested on it vote)