most likely a combination of factors.... when it happened to me I suspected a uncommon phytopathogen
It grew much much too fast to be the trich but may have been a predator of it's spores or feasting on the encapsulated food source (granular only)
Since that occurance I recommend to others not to mix granular in with their substrate. But to only use it in the root zone or sprinkled on top.
But like I said, it was a single occurance and I use trich every single month on all my plants with great results... so i dont know.
Your substrate does look a little funky, but if its been working well for ya then meh....
In cases like this we try to look for a variable that sets it apart from the rest of the group. If none can be found that one can only assume it came with the plant or a unique combination of factors.
Wish I had a black and white answer for ya..
Good advice from some good growers... Hope it helps,