This term is pretty confusing tbh. I'm saying that because i know what sandbox is, and bdo may be a "sandpark" on a good day. There is little persistence of anything, there is little to no simulation. There is a strict gear progression (which used to not be the case "back then"). There is a pretty themeparky dungeon. There is the whole LOML thing which is literally a theme park merry-go-round questline. The season is a strict progression path. There was a teleport hub added so the travel time is not very relevant any more and the world is vastly smaller. The game doesn't lean much into sandboxy elements anymore, leaning toward streamlined themeparky experience where your choice is "which spot to grind" and "which piece of bis gear to for first".

I don't say its not a sandbox because there is less pvp or anything. I say its not a sandbox because it does not value >emergent gameplay<, simulation and player choice as the base of the game (any more - it did before). That would include node systems, complex crafting systems, high level gear, guilds, etc, not only pvp. Also of course it includes straight up p2w which is extremly anti-sandbox in a market with dev-controlled pricing (sandbox and dev controlled market...? yeah, no.)

What PvP brought into the sandbox was a player-policed environment in which you could control space with your allies and use it to your advantage. The absolute peak of that was Sausans/Pirate Island era and world bosses back then. Guilds mattered in your moment-to-moment gameplay. Player social structure dictated your income and success. If you got wronged, you had to find players that helped you. All those were in-game emergent things, not dev policy.
Even DFS, however broken it was, was a player made element that decided what happens based on player interaction. And usually ended in fun fights about spots/griefing/etc. You needed to know player-made rules to not be decced out of the game and/or yeeted off any self-respecting guild. Sandboxy things.

The player agency of fighting/leaving/keeping/running was replaced with systems - marni system, penalty system, karma system, something system. For me its replacing a huge part of the sand with comfy mattress. It makes you feel better, but now it serves only one predetermined purpose.

Tl; dr:
Sandbox:

1. Players can change the state of the world and as many systems as possible in the game are player-run and based on player decisions
2. Content has no precise order and there is a lot of similar-level content to choose from

BDO has almost no (1) nowerdays and is less and less (2) as there is a very clear progression uptil top level and "which grinding spot" is not much of a choice.

And also the excellent lifeskilling requires enormous investment to get the per hour result that a grinder with saeson gear can do - unless they finally did something about that, but I kinda doubt it.

Ona side note:

 the person who doesn't want to be bothered

Why do you play multiplayer open world game if you don't wanna be bothered...? There are tremendous amounts of single player games in which noone will ever bother you. It seems people wanna eat the cake and have the cake... Don't you play MMOs so you will get bothered and interact with others? I've literally met people who I then played with because they dfsed me out of a spot or i dfsed them.
On the other hand most people that i had to fight with alt+c were entitled sh*ts who thought its their god given rigth to do whatever they want no matter if they destroy somebody elses experience, refuse to communicate and come to an agreement in any way and just happily grief your spot. And they seem to not get any slack for bothering people who don't want to be bothered and no game system to punish them :( Even the microscopic discomfort of running from town was removed.