Play the Soprano & Alto lines on a piano:
Can you understand why I find this shocking?
Why—you might ask—is he allowed to get away with this? The fact is, the more voices one adds, the more freedom is granted to the composer. Moreover, in this passage, Guerrero has an amazing canon happening between Soprano & Quintus; so we should cut him some slack.
I’ve seen similar passages by Orlando Lassus—where he technically does not break rules, but the overall effect contains massive parallels.