I have accidentally activated Picture-in-Picture (PIP) mode before. I finally figured out how I actually stumbled upon it in my Philips TV. Just press the "OK" button and give a quick tap to the right arrow.
However, there's something you should know – this method isn't officially endorsed by Philips. So you can't always make it work. It's not a consistently available in all situations, so keep that in mind. While it's an interesting feature to try out, it's not something you can count on every time.