Canada

That's the common journalist error of mixing up power and energy. 1 Watt is 1 joule per second, and is a rate of power. Saying a datacentre will have a daily thermal load of 16 and 18 gigawatts is like saying your car has a daily thermal load of 14 litres of gas per kilometre.

Heat exchange can be given in watts, but again that's heat exchanged per second. If a room has a heat loss of 500w you can maintain temperature by using a 500w space heater on max or a 1000w space heater at 50% power. Saying the room requires 500w of heat daily doesn't make sense.

It's most likely the data centre has a maximum power draw of 18 gigawatts if everything was running at max all at once, which isn't a realistic average use, and also doesn't give an indication of how much heat is being produced.

It seems they got the 23 nuclear bombs by taking the amount of energy the Hiroshima nuclear bomb was estimated to have released (about 63 terajoule) and comparing it to the amount of energy consumed in 24 hours at a rate of 18 gigawatts (18 gigajoule/s × 86,400 s/day is about equal to 63 terajoule × 23).

This makes no sense tho. One sentence earlier, they say: "In all, the data center project will use about nine gigawatts of power using on-site natural gas generators per day, instead of drawing power from an energy grid"

You can't just use 9GW of energy and produce 16 GW of waste heat. That would be a very severe violation of every law of physics I know.