This post was a blatant spam post, initially seeming like a bare link to a Google Drive file, but that was actually a misleading link that went to a spam site (the actual link URL was different from the link title).
Initially, I didn't mouse over the link, and reviewed it as "Recommend Deletion". Suspecting possible spam, I reported it to SmokeDetector (a community-run chat bot that identifies and reports spam across the network), which promptly identified the misleading link after scanning it. I then realized I made the wrong decision by making that review, and cast a spam flag. The post got six "Recommend Deletion" reviews, and got deleted from review. The spam flag was marked helpful as soon as the review completed.
This has several problems. First, as the post was deleted from review, the author is able to undelete it, restoring the blatant spam without leaving much of a trace. Second, it won't result in a block against the user or a -100 rep penalty for the spam. Finally, it's not possible for <10k users to flag it for a moderator to reverse the review deletion and instantly re-nuke it as spam.
Many savvy reviewers are aware of this behavior, and don't issue reviews or delete votes towards spam posts and spam flag them instead. Some go far as to even issue "Looks OK" reviews to stop others from reviewing them (this is a bad thing on sites with review audits, as this will fail the audit). But if the spam is too subtle to notice, reviewers may just take it as a low-quality post and issue "Recommend Deletion" reviews or delete votes. (I didn't notice the misleading link until I had the post scanned by SmokeDetector.)
Many spam posts, especially subtle ones like these, end up tripping the low-quality heuristics and get fed into the Low Quality Posts queue. From there, it's up to reviewers to know that it's bad to issue "Recommend Deletion" reviews against these spam posts, and then the spam has to not be too subtle for reviewers.
Moderator flags are not dismissed automatically, but only by moderators. The best way to fix this, in my opinion, is to do the same for spam or abuse flags: if a post gets deleted, keep any red flags in the queue until a moderator handles it: this way, moderators are aware of the abuse and can change the review deletion into a proper spam or abuse deletion, and decline wrong flags.