We're discussing an off-the-cuff comment aimed at someone across the table while being recorded, which felt very much like the continuation of an argument they had engaged in previously. It wasn't some planned and calculated slight, it was a conversational counter-point.
And it was hardly a gratuitous joke.
First, it was relevant as William Wallace was being brought up as an example of a warlord. The counter was that William never healed anyone and the example of the only real non-fatal injury seen on screen is invoked.
Second, the edition was irrelevant to the discussion as they were discussing the warlord and his place in 5e, not 4e or anything else related to 4e other than the existence of the warlord. Had they been discussing the marshall it would not have been 3e edition warring.
It wasn't even comprehensively related to the warlord so much as a single ability of the warlord. Criticising the 3e ranger for Favoured Enemy when discussing the class in relation to 5e doesn't mean you're an anti-3e edition warrior, it just means you're critical of a particular ability and don't want to repeat any design mistakes.