Is it a metaphor for metamorphosis?

For the form of the change of forms?

A meta-form?

No. It's a metaphor for metaphors.

A meta-metaphor.

Panel 1:
G is pushing a potted plant.
H: Ahhhm ... What’s this?
Panel 2:
G: It’s a plant!
H: Soooo ... why does it have a face?
Panel 3:
G: I don’t know. Why do you have a face?
H: Is there ... some kind of ... point to this?
Panel 4:
G: Well, this is a comic so there has to be some kind of meaning. Maybe it’s something deep and philosophical. We’ll just have to wait and see what happens.
Panel 5:
G and H look around in anticipation.
Panel 6:
The plant falls over and is now lying face down.
G: Right ... face plant.
H looks annoyed.