Well, the article also says that Musk & JB are cofounders of Tesla, so, you know.. Not expecting much accuracy from the rest of it.
I'd agree with you and say they're all cofounders (as, Wikipedia tells me, they settled out of court to agree on). But I think the media really emphasizes Musk, and in this article Straubel, as the co-founders while eliding Eberhard's contribution (ie. actually STARTING the company with Tarpenning).