@taz It isn't really, sadly - 'microdon' is 'microwave', 'popty microdon' is 'microwave oven'. (In North Wales, dunno about South Wales, where 'oven' is 'ffwrn'.)

My Welsh speaking friend explained 'popty ping' as sounding like something a little child would come up with if they didn't know the actual word, and apparently it pisses off some Welsh speakers that it's become this huge meme/joke example of Welsh.

It's a bit like 'Whose coat is that jacket?' which is simultaneously something English people say to mock the Welsh, something Welsh people use as a self-deprecating joke, and something Welsh people might just actually say sometimes.