This is the level chart.
All the first 75 are no-legacy. The next five symbols (the ones without any numbers) are the legacy backgrounds. If you legacy, you will have that background no matter what level you are on in that legacy. The fifth legacy background seems to be what you're talking about.
However, there is a glitch where it show an awry legacy symbol, that's probably how you got it if you didn't have it before.
Glad we could help.