can be easily replicated. trap a bunch of endermen in a space with flowers and grass blocks, they will ignore the grass blocks and choose picking up the flowers over the grass. this appears to work with all flower types except for the 2-block tall ones. they can also pick up mushrooms as well.
This is intentional as these blocks have the enderman_holdable tag by default. See also MC-155758, which describes the opposite behavior and was fixed in a 1.15 snapshot.