In numbers, yes, a rounding error. In fact, SoftBank was one of Nvidia's backers, and whatever this sell means in the stock markets, this is a strong signal.
Daily trading volume is roughly 200m units at roughly 200 USD per stock which equals 40bn in daily trades. So 5bn isn't nothing but over the course of a month it isn't particularly much.
5 billion is massive. So much of that 40bn daily volume is just leverage. Sort of like the derivatives market, trillions of dollars in volume but nobody has that much money, it is just margin. So even if some trading firm losses 1-2 billion everyone panics and goes out of the market. It actually happened during the flash crash.
Also, I highly doubt they sold those 5bn of shares in any exchange. Most likely they did it over several weeks on a dark pool. Because again 5bn is massive and it would cause a crash in any open exchange.
