It’s a named cultivar, most certainly grafted. If it was propagated here in the US, the stock is likely not JBP, more likely Scots Pine. But, there certainly is a big difference in caliper between the stock and scion which will always be difficult to work with.Just a small information. Tree is grafted likely onto Japanese Black Pine. Base is fairly big. That is normally good however base is awkward from presented angle and base will outgrow rest of tree as well as bark not matching. Somehow that must be hidden/deemphasized in development or display of tree. Sorry for bad news. However will leave actual tree development advice to Japanese White Pine keepers.
Most likely will plant on the yard..It’s a named cultivar, most certainly grafted. If it was propagated here in the US, the stock is likely not JBP, more likely Scots Pine. But, there certainly is a big difference in caliper between the stock and scion which will always be difficult to work with.
All we can see from your photo is the trunk coming up out of the soil. No evidence of the nebari.
The OP needs to dig down around the trunk and find where the roots start. They may be just under the surface, or they may be buried several inch down.
Frankly, while I love JWP, that graft union is such I would probably have not purchased this plant for bonsai. As a yard tree, it would be fine.
Good luck!