Even though Luciel knew that the main purpose of Treyton giving such a box away was mainly to prevent the plants from prying on their bed matters, he still made it convenient enough so that Luciel wouldn't refuse it and continue using it.
So, the plants couldn't actually see anything, and even if the plants had indeed seen them accidentally while they were enjoying their time together, it didn't have much effect on the plants at all except for adding knowledge.
Plants have different structures to them and also have different aesthetics. To them, they might just look like plants with just different lines, just like how they couldn't distinguish much of the plants even though they have different lines and numbers of leaves.
So they also wouldn't understand much of what they'd seen aside from knowing that they were doing it because they were enjoying themselves.
