I do not know if it is good for health or not. I am not also that interested in knowing it. It take just few minutes to warm Pizza if it is already  cold. I think such things are done to create more views than something he will continuing using it to warm Pizza.

Radiations are generally used to make food clean from microorganisms. Processes sealed foods undergo radiation which kills the microorganisms in them so the sealed food can last longer. Even Microwave use radiation to warm food.

The microwaves do use an electromagnetic radiation but it non ionizing radiation, it not same type of radiation that is used to irradiate food for killing microorganisms. For that of miner here I do think the bigger concern is how the food is heated and hygiene.

This mining equipment can have dirt and dust around it and it’s heat may not warm up the pizza evenly, so even with the heat itself not being dangerous …… using a microwave, air fryer or even oven is still much more better way to warm up food.

The heat generated from Asic miner is not toxic to environment but what I fear is the conspiracy theories the public might want to draw to this news. If people can believe last year that 5G network was harmful to the body, don't be surprised if people spread informations that his delivered pizza caused some harm to people, this is what I fear the most. That said.

From the OP link provided to the source, he seems to he using car to make delivery and it's the same car that powers the Asic miner using 12 volt from the car and the Asic miner has a cooling fan that maintain the temperature to 40 degree. This doesn't even provide large amount of heat, that's small difference above the human temperature, at least useful for customers than eating a cold pizza.

The high chance of him finding a block is even low, this might just be a Bitcoin enthusiast who found time doing what he loves and as well as minimize cost of electricity to try his luck to get the block reward.