Yes it is. True soap does not become contaminated. What becomes contaminated is the water that was used to dilute a bulk concentrated “soap” product which most likely is not 100% true soap at all. If the water becomes contaminated what it dilutes will obviously also get contaminated. It is the water that is the medium for bacteria not soap.
Also it is the dispenser knob that gets contaminated.
You touch the dispenser knob before you wash your hands.
So how does fecal matter get up into the collapsible plastic bag that holds the soap? That would be some trick.
I’m just not buying it.