Ok, perhaps I can provide some guideance here.
Shohin: yes, the most generally accepted definition is that it’s a bonsai under 20 cm (8 inches), in height.
Now, be aware that also includes “bonsai” in the definition! Bonsai, while literally translated means “tree in a tray”, we all know that it’s more than that.
What the OP has is a two or three year old grafted JWP. It, unfortunately, is al least a decade away from being any semblance to a bonsai.
JWP are slow to develop mature bark, and develop the taper, ramification, and character we associate with “bonsai”. This one is a graft, and is so young, the grafting scar hasn’t even fully healed yet. The stub from the root stock is still sticking out!
Now, I’m not trying to be snobbish, arrogant, or insulting, I’m just trying to share wisdom and experience of having worked with these little trees for nearly a half century.
Putting it in the ground may very well be the right thing to do! Just put something around it so you don’t mow it over!
I don’t think this particular specimen is a good long term Shohin candidate, but it could make a nice medium size tree in time. As Frank said, the first branch is too high off the soil line. With Shohin, we want that first branch to be low, like at the 2 inch level!
And, we only see the portion of the trunk that is JWP. There’s a grafting stock trun under the soil line. Where are the roots? The real nebari? Finding that out is vitally important.
Next, the internode lengths. Pines of all types tend to grow up by sending up a candle. The candle sprouts the needles, and at the top of the candle, it produces buds for next year. These buds usually have one main central bud that tend to grow straight up, and a number of secondary buds that while the grow up, too, they get forced to grow out sideways. These eventually grow into branches. So, a series of whorles develops as the tree grows taller. You can get a very accurate estimate of the age of a tree by counting whorles.
For bonsai, we want the lengths of the internodes between whorles to shorten as the tree gets taller. Unfortunately, young trees that are just starting to grow tend to have lengthening internodes! Just the opposite of what we want in bonsai! This tree is exhibiting exactly this behavior. So, what do we do? Cut off that long trunk section? Well, if we do, that will retard the trunk girth development! Right now, that trunk section is the strongest, and is providing the sugars to fuel the tree. Cutting it off will slow down growth. But, isn’t that what we want? Not really, slowing the growth will keep the trunk thin. Which will make the tree look like a very young tree.
So, instead, I recommend that the section be kept as a sacrifice to fatten the trunk, and designate a branch to be trained to take its place when the sacrifice is removed. When will it be removed? I don’t know, when it has “done its job”. One caveat: don’t wait too long, or else the scar will be huge!
This process of growing out a sacrifice, cutting back, growing out another sacrifice, cutting back, can go on for several decades!
Anyway, I thought I’d give everyone a bit of food for thought.