Frankly, I DO think it was DELIBERATE.
If you look at the OTHER mannequin, its neck top is FLAT. If the red plant is BEHIND the dress statute, it would seem the dress neck top should be flat too.
Also, if you look at the EDGES of the plant you'll see that they are INSIDE the neck. Imagine if you took the plant stems and put them IN a thick vase. You would not see ANY stems DIRECTLY ABOVE the sides of the vase.
I'm assuming the TOP of the neck is REMOVABLE, so the store can add a head or not. So whoever set it up left off the top and stuck the stems IN the neck.
I tried Google and Bing image searches and only found ONE image between both.
I'm guessing that this was a joke set up by whoever set up the mannequins, then the person took a picture, and then took the red plant out from the neck. If this was left as shown there probably would be loads of photos on the Web.
Plus, it looks like a fairly upscale store--not the kind of place that would let something like that stay up.