More official advice completely divorced from reality
That last bit of advice is a bit hard to swallow: your correspondent, as do millions of others every day, works on a laptop with a mains connection.
Too true. Does any government official ever consider whether people's bullshit detectors will fire when spouting crap like that? The issue here is dangerous chargers, not using devices while connected. Logically there is no real difference between using a mains-powered device while it is attached to the mains and using a portable device while attached to the mains. If anything the later is probably safer.
But no, admitting that you can't enforce the law properly and keep unsafe kit off the market wouldn't look well, so you get crap like that instead. Keep it simple and aligned with reality - i.e. "Buy from reputable sources, make sure the device has these markings" - and you stand a chance of people paying attention. Load it with bull and the end result is the entire message gets disregarded.