It's not truly safer. It's just smaller, and only has open-source apps. So it's harder to hide malware, but still certainly possible (nobody checks most apps).
The issue is the "finely curated" statement. It's not a full code review, just "Wherever possible, applications in the repository are built from source, and that source code is checked for potential security or privacy issues. This checking is far from exhaustive though, and there are no guarantees."[1] After an app is added to F-Droid it gets built from source by the F-Droid build servers, but it does not generally get re-reviewed. It's perfectly possible to add the malware after the initial release. It's also possible (even easy) for malware to be missed by the limited code review. F-Droid is a little safer, but that doesn't mean it's particularly safe. It's no harder to get malware on F-droid than it is to get it into Arch or Debian or any other distro repository.
