I'm sorry but that explanation is factually wrong but sadly this is what is being pushed by spanish politicians and media alike so it's no wonder foreign press got it wrong too.

Consent always has been an important point when judging sex crimes and the scandal of the Pamplona gang rape which sparked the new law had nothing to do with consent (the victim not consenting was never in doubt, otherwise there would be no crime) but with the aggravating factors. Both the initial court and the appeal court decided that the actions didn't qualify for agresion but for the less severe felony of abuse. Note that both abuse and agresion can qualify as rape or not and it was just a choice by the lawmaker to explicitly not use the word "rape" except in one instance.

Feminist groups got upset either by ignorance or by populistic takes on the matter and the slogan "it's no abuse, it's rape" became popular. But aggresion wasn't equal to rape but rape was an aggravating circumstance for both sexual aggresion and sexual abuse. The solution in the new law was to eliminate the "sexual abuse" and combine both abuse and aggresion into one felony. But by doing so they also combined minimum and maximum sentencing from the old crimes into the new one.

The spanish criminal code establishes that any new law that is more favourable to the offender has to be applied retroactively. The problem isn't per se that the minimum sentences have been reduced but that, by doing so, if the same crime was judged according to the new law and keeping all other circumstances the same a lower sentece would have been handed.