So I was on this drawing app, and I was viewing someone’s portfolio and the drawings are in rectangles.?

And I don’t have auto lock on, I turned it off so it wouldn't fall asleep (I have an iPhone) and I had closed it, and went to another app, and I could see the portfolio very lightly as if it’s still there. I don’t know if this makes any sense, but I don’t know what to do about it.