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.
If Frieza knew of SSJ God he heard it passingly in one of his rare interactions with Beerus. And Frieza probably feared BOTH- the super saiyan emerging, as well as the super saiyan god. Due to the fact that god ki wasn't a plot device at the time- we focused and only heard of him knowing and fearing normal SSJ at the time. But who are we to say as viewers that Frieza DIDNT know about SSJ God and it just wasnt focused on? For all purposes, he shouldve known. I have no doubt Beerus, despite being as narcissistic as he is, wouldn't mention the potential destruction of his omen when frieza mentions the destruction of a certain sector that contained a certain saiyan planet. We know now that Frieza could not have done all the destruction he did without at some point interacting with Beerus. And we know cannonically he has met beerus at least once. So. It's all pretty safe to assume.