Heres a quote right from the promix website. I just copied it and im pasting it so you dont think that the real growers are lying to you still.
PRO-MIX® PG ORGANIK™ is formulated with fine sphagnum peat and fine vermiculite, similar to our
PRO-MIX® PGX to help with water retention for emerging seedlings. It also contains coir - horticultural grade for improved water absorption of the growing medium, even after the wetting agent is broken down or leached during extended crop cycles. Also added are limestone (for pH adjustment),
an organic wetting agent and a starter fertilizer that lasts approximately 2-4 weeks.
I mean if it was just an inert substance like clay pebbles, or lava rock, surely you dont believe it could sustain plant life for 2-4 weeks right? There must be some organic matter AND some teaming with microorganisms going on in that soiless blend of soil right dave?