EDIT: Also few (I don't think any but again I can't remember all the details) of the witnesses claim it to be a hoax in testimony as you are trying to represent - most of them simply say that they can't confirm an actual chemical attack took place and that the symptoms of victims mostly don't match those of a chemical attack - they don't offer an opinion on whether they thought it was real or staged.
I should have been more accurate on the terms they used. I should have said they didn't believe the White Helmets and saw no evidence of CW use or symptoms. Amounts to the same thing.
If they didn't think it was genuine then what is it other than a hoax?
They did offer opinions by the way.
The first, the father of the famous boy hosed down, said it was fake and there was no CW attack. He was angry his son was taken without his permission when there was nothing wrong with him.
The second, a doctor on duty that night, said people came in for smoke asphyxiation from a nearby house that had been shelled. He was clear it wasn't a CW attack, but then the White Helmets barged in shouting 'gas' and dousing people with water. He didn't believe them.
The third was someone who came in for smoke inhalation. Supported what the doctor said saying the White Helmets rushed in creating chaos dousing people with water. Said they all looked fine and couldn't see anyone suffering from anything that looked serious. Didn't think it was a CW attack and smelt nothing unusal (no chlorine then).
The fourth was a lab technician on the night. Came out - same thing. Said smoke inhalation victims, but WHs causing chaos. Saw no signs of CWs and that if it was they would have been affected too as they had no protective clothing on. Didn't believe it.
The fifth was a nurse on duty. Didn't believe it...said people came in for smoke inhalation then the WHs shouting causing panic. Checked a girl and no signs of CW exposure. Didn't see anything indicating that.
On and on it goes. Smoke inhalation victims then the WHs come in causing chaos and panic, but no signs at all of CW or chlorine exposure.
Matches up with what Robert Fisk reported speaking to doctors shortly afterwards.
Those people are medics in a bombed-out city. They know smoke inhalation when they see it and they didn't believe the source of these claims, the White Helmets.