Hello,
Avast RHEL package is still being built on centos 6 and it should work on RHEL 6 and 7. We do not yet support RHEL8 due to CentOS 8 not being available yet. I am not sure about what is written on the web, however we will continue supporting RHEL6 until 2020 when it's support ends.
Kind regards,
Ondrej Kolacek