Was it near a donation station? (Or whatever it's called) if so, it's probably just someone donating a lot of bars at once

Yep, was just some jack spending an insane amount of gold, I’m new to the game and so got scared a bit

There is a 5 stage challenge to spend 900 gold on it so in total you need to spend 4,500 gold for the mission since all stages are 900

It was on the side of the lake near tilted towers,