You would ingest more chlorine in the water you drink cook and bathe in, swimming pools plus from many other house hold cleaners Etc, than what you are likely to get from what is happening with that laser cutting the PVC sheet, what I could see in the photo there is nothing that is toxic, it may smell bad but is not a problem for your friends
[I envy your ability to identify toxic gases from photographs.]
Chlorine Gas does not float up in the air like you can see in your photo, Chlorine is heavier than Air so sinks down to low areas Like floor ground level
[Even things that are heavier than air can form clouds that can poison you before they settle out.]
Everyone in the shop would either be dead or very sick if there was any Chlorine in the air
[You've never heard of sub-acute poisoning?
https://www.ncbi.nlm.nih.gov/pubmed/29775917]
The add Chlorine in PVC is a flame retardant to prevent it from burning
[But when you burn it anyway, bad things can happen.]
How is Chlorine made
Salt (sodium chloride) obtained from dried-up sea beads is dissolved in water to form a solution of brine. This solution is placed in a cell and a current of electricity is passed through it. Chlorine gas bubbles off in one part of the cell and sodium metal is produced in the other. The sodium reacts with water to form caustic soda (sodium hydroxide) ( Drain Cleaner one of the uses) and hydrogen gas. Both of which have important commercial uses.