My adult bp who I have had for 5 yrs did this his last yr in his AP cage ( he is now in a rack ) he had the same hides on both sides and had always had the plastic plant behind his cool hide for the 3 yrs he was in the cage. Then one day he just started using the plant as a hide he did this for about 3-4 mos then went back to using his hide.
Nothing in the cage had changed prior to him using the plant and nothing changed while using the plant. His cage was the exact same for the enite 3 yrs he was in it.
I figured he just got bored and wanted a change of pace.
Just keep an eye on yours. Long as he is eating and temps/humidity are constant I wouldn't be to concerned.
Try and keep your cool side at least 80. 78 is a tad cool.

Hope this helps.