In the Dragon Ball Minus manga which is part of Jaco the Galatic Patrolman if I understand correctly, Frieza knows super saiyan god. But in the anime series he seems to know anything about him, since he feared super saiyan and not super saiyan god, which doesnt make sense if he knew super saiyan god who is much stronger. So my question is, is what Dragon Ball Minus says canon? Did Frieza know super saiyan god? Sure not all official Dragon Ball mangas are canon, because some contradict the series like the Dragon Ball Heroes manga or the Dragon Ball Gaiden manga.
The Super Saiyan transformation was considered to be Godly and legendary as it was something which was considered to be nearly impossible for a saiyan to attain. This was what Freiza knew off and also what Vegeta knew off. This is the transformation Vegeta kept referring to and knew Goku had become one, once he saw him on Namek. The concept of God Ki and the new transformations are things which have been introduced very recently. Also, since Freiza hadn't trained with either Whis or Beerus, he has no perception of what God Ki is, as it's been stated multiple times that God Ki cannot be sensed like other forms of energy.
Freiza's golden transformation is an immense multiplier which makes him as strong as Super Saiyan Blue Goku, however, it's not utilisation of God Ki as many fighters like Krillin, Vegeta, Tien and Roshi were able to sense Freiza's energy. I think it's fair to assume The Super Saiyan transformation was something which was considered to be very godly then and it was that what freiza was afraid off. He had no idea about any other Super Saiyan transformations, not even SSJ2 or SSJ3 which happen to be weaker than SSJG. We know this because Freiza asks Goku to turn SSJ during their rematch in the ROF arc and Freiza was only aware of that transformation.