Elastic doesn't provide FreeBSD packages officially. So you won't find FreeBSD packages on the download pages. If you want to run it on FreeBSD then I recommend building from source using the release branch.
The packages located at https://beats-nightlies.s3.amazonaws.com/index.html?prefix=jenkins/filebeat/ are built from the master branch (no stability guarantees) whenever a change is committed. They are published by Jenkins for convenience and testing purposes.