And calling the Western Roman Empire illegitimate (even though it contained Rome) and then the Ottomans too, but calling the Russian Empire (which never had anything to do with the Roman Empire) legitimate is more than questionable.
I mean, obviously it's a joke chart so it stretches interpretations to get the conclusion/punchline, but it might mean 'illegitimate' because, as it notes, the West was 'reunited' (extremely temporarily) with the Eastern Roman Empire, and the ERE always claimed to be the 'one' true legitimate Roman Empire.