Earlier quoted context omitted.
You are spending fiat though with that debit card, like every debit card. Transactions are off-chain.
That makes absolutely no difference whatsoever. By your logic, people using coinbase to hold their coins aren't holding bitcoin. It is exactly the same. Bitcoin from my wallet is being spent. It is increasing in value while i don't spend it, because it is in bitcoin. It is no different than an American using their cc in europe.
Exactly, they aren't. Coinbase owns the private keys, thus the bitcoin.