pl0x Maestro, Mastercard Debit and Mastercard Credit are three different things. And bunq's card used to be Mastercard Debit, then they switched them to Mastercard Credit. They're also still offering Maestro cards. But most of bunq's cards are actually chipped as Mastercard Credit nowadays, not Mastercard Debit anymore. (Some might still exist because customers still use them and they didn't expire yet.)
Maybe they will re-introduce Mastercard Debits when Maestro is gonna go away next year, but the Mastercard Credit is here to stay I think. (Just because bunq is from The Netherlands and not glorious UK doesn't mean they don't understand what a credit card is... they are actually a bank cooperating directly with Mastercard)