Interesting, I'm going to ask people about it and it's context to see if anyone I know tries to justify it.
I expect the context is that it was the 50s 60s and 70s and the dodginess of Iberian politics in racial terms was found in nationalist parties of both kinds, both Spanish and separatist. I bet I can find some nasty Spanish priest of the same eras saying much the same about Andalusians.
It's not that surprising to see the Catalan right having much the same worrying skeletons in its closet as the Spanish right does (the mere fact of their being Catalan neo-liberals with a murky back-story does not make them an improvement on the Madrid version) but the ERC's championing of a rightist catholic nationalist priest is harder to comprehend.
Though lots of sound Basques say of Sabino Arana that although he was a suspect racist hijoputa he was their suspect racist hijoputa. Maybe that's it.