I was thinking the same thing. That one accelerates its growth in the presence of radiation. But it also seeks out human flesh and brains to build its biomass intelligence blob, unfortunately.

In the books, it is suggested (if not stated outright) that the protomolecule was probably intended to work with much simpler forms of life, but is also able to make use of higher forms like humans.

The reason so many were infected on Eros was because humans deliberately infected everyone on the station. Likewise with the human/protomolecule hybrids.