Nowhere in his post does he say he is using back flow preventers. Maybe a new torch set comes with them. I haven't had to buy a new set of regulators in the last 45 years.
This isn't worth mentioning to you, but if he doesn't have flash back arrestors and he did not close the acetylene valve on the torch handle. He then closes the oxygen valve on the bottle and opens the oxygen valve on the torch handle fast if he is running a lot of oxygen pressure, the oxygen could go back into the acetylene line.
Because of a situation like this is one of the reasons they made back flow preventers. I think the flash back arrestors have a back flow preventer built into it also.
Have a nice day Mr. Stick. Beat up some one else for a change.