Bitcoin is also reversible before 1 confirmation. Till now I saw only perfect money is irreversible. Anyway, crypto is yet still best but for btc need at least 1 confirmation. For other crypto need to check how many confirmation is needed for approved. Once confirmation complete then there will have no option to make reverse.
of course, 0 confirmation need these input can be used again "double spends attack".
this is why before a btc payment is "confirmed" people accept as convention at least 1 confirmation (or even 6-8 confirmations it depends the service you're using).
Paypal is ALWAYS reversible as any other service that use a Credit Card since any user can claim a "chargeback".
Probably these are the real owner of the accounts that make this claim and receive money back after they recognize to have been scammed.