The KNB guy was pulling your leg or it was a load of BS. Neon is a gas! Excited by high voltage electricity. It is amazing the urban legends that persist on stuff like this.
I showed McTiernan the green Cylum sticks and suggested they be used as blood. The DP said it isn't bright enough to photograph. I said, your right it isn't, but here’s a trick. I cut open the stick, poured the contents in a cup and popped it in the microwave for a few seconds. Presto, bright as a 40 watt light bulb.
To which the DP replied, "We won't have microwaves in the jungle." “No, but you will have hair dryers!” I replied. So that is what was done (according to Kevin Peter Hall) hair dryers where held on the "blood" until the camera was rolling and presto, bright green glowing blood.