Yup, it's hazardous terrain that is within 3 of the Crypsis Core, so it makes an 3 area of hazardous terrain. However, this means there is now another piece of terrain in base contact with the Grave Goo, so that means that the 3 area around the crypsis core is also hazardous to it's own crew.
And what's aggravatingly non-specific about "terrain in base contact"? It's as specific as it needs to be, it only affects terrain that the goo's base is touching.