It is real. If you search "coconut crab" online, you'll see pictures of crabs of this size. They're amazing! The Wikipedia page says this species can grow up to 40 cm, 4 kg, with leg-span of 90 cm; but they only grow that big after more than 40 years.
This picture is very possibly real. The coconut crab is quite widespread in those Southeastern Asian countries, so I don't know if there're subspecies that grow bigger than the ones in Lan Yu. The general description matches the size in the picture.When I see giant arthropods, something about their legs and exoskeleton just makes me wanting to take them home! (But it'll be tragic to be pinched by their claws!)