I have scatterplot in Tableau, and I displayed trendlines. However, I cannot understand why there are three of them.

When I research this on Tableau, they say the upper line is upper 95% confidence, and the lower line is lower than 95% confidence.

When I think of confidence levels, I think if there are 100 black and white marbles and I take a sample and see the ratio, I can say 95% of the time, white marbles will be 40% to 60%

And to create confidence bounds, 92% to 98% of the time, white marbles will be 40% to 60%

But I'm having difficulty translating this to tableau trendlines. Please advise.