The true meaning of what Bluehost said is “we don’t support Let’s Encrypt. You will need to get a certificate from a third party and then you can install it via your Bluehost account”.
Something to understand is that Let’s Encrypt is meant to be automated. The ideal way to use it is that Bluehost should integrate it into their hosting services, and you shouldn’t need to do anything manually. There are many web hosts that support Let’s Encrypt properly, but Bluehost is not one of them. Often web hosts do not support it due to a profit motive, for example, if they charge money for SSL certificates.
The problem with this is that Let’s Encrypt certificates only have a 90 day duration. So you would have to continually re-issue the certificate via ZeroSSL and re-install it to Bluehost, at least once per 90 days. Not very convenient, I think you’d agree.
ZeroSSL allows you to issue a Let’s Encrypt certificate manually using your web browser, which you would have to import to Bluehost by hand.