Without context, you could interpret the response like you did. But let's be clear: moderators are not exempt from any rules we have here—whether it's about quality or behavior in general. Feel free to flag a post when you see something wrong. We occasionally have to delete (older) posts of other moderators for quality problems or other issues. And we try not to handle flags on our own posts either, for obvious reasons.
Back to the topic. Your flag reason was:
spam answer that goes to user's blog
Seeing that in context makes it clear why the moderator who handled your flag chose to answer like they did:
Post does disclose affiliation with the link.
That's one of the most important criteria when evaluating possible spam posts. Generally, we let posts pass when they're actually useful and the author discloses their affiliation. Of course, that doesn't mean you can get away with only posting about your product or website. But if you're honest about it and your post doesn't just include a link, you're generally fine.
How to not be a spammer outlines these rules, too, in case you're interested.
Also it's from 2009, back when HowToGeek was an SU moderator.
This part clarifies the fact that it's not just some user that only visited Super User to promote their product.
And you're of course right. It would be better to replace all indirect links to blogs that describe some tool with a direct one, if possible. With The How-To Geek it's a bit of a peculiar thing since he has a popular website with (generally) helpful posts. Those are easy enough to link to, and it's not very likely that the website will become unavailable any time soon.
Please keep in mind that he hasn't posted an answer since 2009. Back then, our quality standards were quite low compared to today. We still keep finding old posts that need to be cleaned up.
I'd also like to point out that we shouldn't just hunt down old link-only answers to delete them. That's the easy way out. But if those have upvotes and we know that they solved many users' problems, deleting these posts does more harm than good. They should really be edited to include the important parts here—at least if it's possible to do so without major efforts. And this is something you can even do yourself! You don't need a moderator to do this.