Apparently the original plan was to deplane normally via steps. Steps were requested and you can guess the rest. The situation viz pax began to deteriorate and it was only a matter of time before somebody took matters into their own hands.
No, I wasn't there.
The introductory blurb in the 757 QRH sates that 02 and goggles should be used if neccessary. No idea about masks on anything other than 757/767 but they are a serious barrier to effective communications.
As an aside, only 2 of the 200 odd pax declined to continue their journey with TOM later in the day.