Gardeners, will this produce some weird hybrid?

I think it would be alright. Most fruit trees (for both commercial and home use) are grafted onto another type of root stock. If you plant a seed from one of these trees, it will likely revert back to the root rather than the fruit.

I am not an expert (or even an advanced amateur), but my first thought is the potato is simply acting as soil.

@jaytkay The potato is acting as a root, extracting nutrients and water from the soil.

What color is the rose?

Potato + Rose = Prose

If the rose were purple, you would have Purple Prose.

Rooting a cutting is not easy and often a hit and miss mostly because of the cutting becoming infected. There are all sorts of procedures, rooting powders that you can employ and in my experience with marginal results. This potato hack serves 2 crucial purposes. Placing the cutting stem in the potato protects it from infections and also provides moisture and nutrients the cutting needs to grow it’s roots. IMO it is brilliant and gonna go cut some cuttings and give this a try!

I did wonder about the acid in the potato. Won’t it hurt the stem?
@Crusier I thought so to.

@Pandora After I answered it dawned on me that wouldn’t the potato sprout and grow as well?

@Cruiser Yeah, I wondered about that too. Potatoes have eyes that can sprout any place. So I wondered once the stem of the plant grew roots in the potato, you wouldn’t want to cut it out. So does the new roots just use up the potato like a leech, or would they both have roots.
I have a plant that grows peppers and I want to try this out but I wonder if it will just be more of a problem.

From what I’ve heard and experienced with trees grown similarly from root stock, the root (in this case, the potato) is so “busy” supporting the graft (in this case, the rose) that even if it sends its own roots out, it will still be supporting the graft. The only case I have heard of reversion to the root is if the seed is planted. A friend has a tree in her yard her son planted many years ago from a peach pit. The fruit is something like a plum/peach/apricot, and it doesn’t taste very good.
(The only reason she keeps it in her yard is her son is now passed.)

This reminds me of the fact that for 130+ years almost all French wine grapes have been grown on American roots.

A aphid from America almost destroyed the wine industry. The solution was grafting the French grape varieties onto American roots, which could tolerate the aphids.

The Great French Wine Blight