Not sure if you have confirmed this or not yet, but I came across the same thing. The Internation Compensation page on their site still has it listed as the usual £50 compensation with the option of purchasing up to £250. Tracked, Signed, and Tracked/Signed are all lumped together in the same category.
https://www.royalmail.com/international-compensation
I would assume it is a mistake on the pdf (it wouldn't be the first time!) but then you would also have to question whether the information on the site linked above is correct if you would also question their official pdf price guide. Gut feeling says it is a pdf mistake as it makes no sense to remove all compensation from a singled-out international service.