The first Tosafos on Daf 5 points this out. In the second definition of the Machlokes — that they argue about Shaas Vestan — the Braisa can only be Reb Dosa, since it says that Shelo Beshaas Vesta she is Tamei Me’es La’es. Obviously, Beshaas Vesta we say Dayan Shaatan, which is Reb Dosa.
When the Gemara says that the Braisa is Kulei Alma, it is only in regards to Shelo Beshaas Vesta being Tamei Me’es La’es, says Tosafos.