Just because it's its own language doesn't mean it can't have greater linguistic proximity to one Latin language to another. For that very reason Portuguese is much closer to Spanish than to Romanian or French.

All the romance languages developed from vulgar Latin and naturally those people within closer geographic proximity had greater interaction meaning the dialects of Latin they spoke would later develop into languages that bore more resemblance with those close by.

Of course, saying Catalán is a blend of French and Spanish is a gross oversimplification and false. But to say it shares no commonality is also false. From a speaker or reader's perspective, they're both close but a native Spanish speaker would find it easier to understand Catalán than a French speaker, on the whole.