Nova probably missed that it was a burn post, depending on the frontend he uses, they don't all show it.

The self voting prohibition stems from the view that self voting is seen as greedy as you have taken both halves of the rewards.
But, on a burn post, that is not true.

The custom of not selfvoting was a large experience learned by most when they get here, so they share it as a big deal in their hive journey.
Most learned by getting flagged for doing it themselves, or saw others.