I certainly haven't seen that interpretation before. You only get one bonus action per turn. period. Two weapon fighting just gives you something to use that bonus action for. If it worked like you are arguing, then the limit on bonus actions would be pointless, because every specific example would trump it.Ah, I see they Sage Adviced this one. However, their wording still isn't airtight:
Two-Weapon Fighting (under melee attacks, not the fighting style, not the feat) says "When you take the Attack action and attack with a light melee weapon that you're holding in one hand, you can use a bonus action to attack with a different light melee weapon that you're holding in the other hand."
It says when you take the attack action you can use a bonus action. It doesn't say you can use a bonus action if you have not already used one on your turn. I'd even read it to mean that if you have spells and want to cast healing word as a bonus action, then attack with your action, you'd still get the off-hand attack, because it's automatically granted. I'd argue that the specific rule for two-weapon fighting trumps the general cap on bonus actions.
If they really want to eliminate the controversy they need to add a sentence in the PHB like "NOTE: Action Surge does not grant a second bonus action off-hand attack for two-weapon fighting."
Everything obeys the general rule, unless a specific rule says otherwise. The rules for two-weapon fighting don't need to specify that you can't do it if you've already used a bonus action for something else. Instead, the rule would specifically tell you if this did not count for the number of bonus actions you are allowed.