I think the answer is "it can be, depending on how you do it".
For clarity "peng" can have 2 meanings - either "Jin being used in an upwards direction" which is directional, or alternatively a kind of all over "basic Jin" which is channeling the ground force in whatever direction to meet the incoming force. I'm thinking of the the 2nd meaning - "basic Jin", here.
In the video by Rory, he uses frames by keeping the arms locked out straight - this is not like basic jin use in Chinese martial arts. It's quite "hard". However, when using Jin you can learn to not "lock out" your arms and achieve the same results though a connected structure and a channeling of the ground force to the point required using the intent (Yi). This is "softer".
If you can do it standing, then you can learn to use it on the ground. (In theory).