Direct answer
Page caching stores generated pages so WordPress does less work per visit. Object caching stores repeated database results or application data. A CDN serves static assets or cached pages from locations closer to users. They solve related speed problems, but they are not the same layer.
Why it matters
This answer helps site owners locate the real layer of a WordPress problem before applying a fix. WordPress issues often sit between hosting, DNS, themes, plugins, performance, accessibility, backups, schema, content and support responsibility.
What to check
- Is the issue caused by hosting, DNS, WordPress, theme, plugin, cache, content or custom code?
- Is there a current backup and rollback path?
- Does the fix reduce risk or only hide the symptom?
Common mistake
Installing another plugin or changing hosting before identifying the real failure layer and protecting the site with backup and rollback.
Caveats
Low caveat risk: suitable for publication from the available source pack, but still avoid pricing, guarantees, unsupported service promises or claims not visible in the linked public ecosystem.