They are either thinking of Vladimir Komarov (who died during Soyuz 1, in 1967 - six years after Gagarin's orbit, for whom Gagarin was the backup crew) or referencing the conspiracy theory that the Soviets tried a couple times to orbit a human, covered up initial failures, and only made Gagarin's success public because it worked.
Afaik there's not any evidence of this. The Soviets did have a bent towards secrecy so it's plausible, I guess, but it's definitely more the realm of creepypasta ("there could be dozens of old Soviet capsules in orbit with corpses inside!") than historical fact.
