Hearing this doesn't surprise me at all. From my experience, loaches certainly fall under the category of wolves in sheeps clothing.
I've had my 75 gallon loach tank set up for about a year now. On more than one occasion I have witnessed both clown loaches and yoyo loaches chasing after my (former) parrot fishes. The loaches would place their mouths within the parrot's gills and either flash their spines or appear to be biting the insides of their gills (i heard the clicking sounds that normally accompany them eating a treasured food). There wasn't much I could do about the blatant aggression as my 75 is the only tank im allowed and not many people are interested in rehoming a mated pair of parrot fish even if they are free...
RIP Mo'Mo & Freckles
So to answer your question, yes, I'm sure that the loaches played some role in the killings of the others be it from unchecked aggression, stress, not feeding, etc.