I think all three of the trees in this Penjing water planting above would qualify as bonsai on their own and there are some bonsai plantings that might share some rock features with this one

The overall arrangement above is easy to identify as Penjing, No doubt the low white tray helps, but there's something a little more difficult to put your finger on. Perhaps the way the rocks are put together and more importantly, the overall sense of scale and wild ruggedness that is common in Penjing, which seems to specialize in these panoramic landscapes

Not that there aren't bonsai that head in that direction, especially some saikei, but Chinese (and perhaps Vietnamese) penjing seems to say it best. And of course there are plenty of Penjing that don't emphasize the landscapes as much as the individual trees, some of which are almost indistinguishable from Japanese style bonsai

So in answer to the question posed in the title and because I'm in no way an authority on the topic, I'll take the easy way out and leave it up to you. And if you need some help, perhaps you could consult someone like Robert Steven, a person who has spent a long time studying, practicing, teaching and writing about bonsai and penjing arts (stay posted)

This one, which happens to one of my favorite Penjing plantings, seems even larger in scale as the one above and also has a couple human features that set it apart and enhances the feeling of a vast natural setting. These little human or human structure figurines (like boats and huts) are common in certain types of Penjing and much less common in bonsai, though you may see them in some saikei plantings

My apologies for lack of attribution. I found these two Penjing landscapes several years ago on fb and featured them on Bonsai Bark (though the text is all new today). I'm not so sure that our source (Pham Thai Bihn) was the artist for either one (see link below).