You're not wrong, that interview has no predictive value as to gamesas's policy, being by a relatively minor ex-employee. But feathers get ruffled when you raise up "canon" and "ex-devs" in this forum. You're probably not in-tune with that, but some people (moderators included) have said some pretty hurtful things about some pretty excellent people - people who deserve our utmost respect - under the guise of talking about what is and isn't canon.
Comments one whether something is canon or not says nothing about it's quality. There are several excellent moments on these forums, such as the Trial of Vivec and Loranna's RPs, which weren't canon (at least at the time) but still wonderful additions to the lore.
As for Douglass Goodall, I talked with him often here when he was an active participant on the forums and even pvssyd with him several times on LiveJournal. I'd never want to insult or degrade him and I hope if he ever did feel that I was treating him badly he'd let me know - although I realize while saying this that it's unlikely he'll ever see something I type. That's rather disappointing really, it would be nice to have a conversation with him now that I'm more than a teenage college student.
I will note that calling him a "minor ex-employee" seems quite unfair given that he was one of the three primary designers working on Morrowind.
As for canon, from my understanding Bethesda defines canon as anything in an officially published product. Any peripheral content, regardless of author, is non-canon. It is certainly possible for something to be included in a later game or other official media which would then make it canon, and this has happened before. If you wish to discuss the issue of canon further I'd prefer a PM as continuing it here would be off topic.