First Vampire Drain Life, str or cha accuracy?

Level 3: Drain Life

You gain an innate power to drain life from the living. When you take the Attack or Magic action, you can use a Bonus Action to make an Unarmed Strike. On a hit, the target takes 1d6 plus your Charisma modifier Necrotic damage instead of the strike’s normal damage.

Warlock patron From the Grim Hollow material, am I meant to interpret that the ability will let you use charisma stats for the damage of this bonus action ability BUT use the strength stats for the accuracy  roll of the unarmed strike? This seems to be what the DND beyond code does on an actual sheet with this ability.

Or is it supposed to be using charisma for the accuracy and damage and it's just a code error of some kind?

I think the intent is similar to the Unarmed Fighting style feat:

When you hit with your Unarmed Strike and deal damage, you can deal Bludgeoning damage equal to 1d6 plus your Strength modifier instead of the normal damage of an Unarmed Strike.

Or Enhanced Unarmed Strike (Tavern Brawler):

Enhanced Unarmed Strike. When you hit with your Unarmed Strike and deal damage, you can deal Bludgeoning damage equal to 1d4 plus your Strength modifier instead of the normal damage of an Unarmed Strike.

So, it supposed to be using Charisma instead of your Strength modifier only for the damage, not for the attack roll.

EDIT: for clarity.

This is similar to how the 5.5e Dhampir species' Vampiric Bite ability works; it uses Strength for the attack roll but Constitution for the damage roll. Attacks that use different ability scores for the attack and damage rolls are incredibly rare, but they are out there.

Just as an example, a feature that lets you use the ability score for both attack and damage rolls would be Dexterous Attacks (Level 1: Martial Arts):

Dexterous Attacks. You can use your Dexterity modifier instead of your Strength modifier for the attack and damage rolls of your Unarmed Strikes and Monk weapons. In addition, when you use the Grapple or Shove option of your Unarmed Strike, you can use your Dexterity modifier instead of your Strength modifier to determine the save DC.