However, redditstatus.com shows no incident reports and shows error rate as having reduced.

Because it's just Reddit, it doesn't matter.

But it would look bad if this was from a commercial SaaS. Comes across as either shoddy or dishonest.

Every SaaS today depends on lots of 3rd party infra - CDN, DNS, AWS, payment gateways, search engines, and more.

My question: Are there any architectural patterns in monitoring / observability to reduce such mismatches between reality from user's perspective and status pages from service's perspective?