Since you asked I will share some wild speculation, but to be clear I don't know how Apple's fraud prevention works.

Gift cards are the currency of modern confidence scams. Accounts that redeem a lot of high value gift cards are suspect for that reason alone. Buttfield-Addison makes it sound like this is common practice for him, so his account may have been on a shitlist already.

Apple may be so sensitive they'd close a suspect account after one failed redemption. It's also possible that card was first redeemed by an account that was closed soon after for fraud, and Buttfield-Addison's subsequent attempt linked his already-suspect account to the fraudulent one resulting in automated actioning.

Again, this is pure speculation, and is not meant to justify Apple's actions.