Is this Sri Kemban Starfruit grafted?

[Aristolochia]

I bought a grafted Sri Kemban Starfruit tree from Ong’s nursery about 2 years ago when I was still getting into growing. I also bought a Fwang Tung (grafted) about 6 months ago (shown in the first pic with the clear graft and fruit). They’ve been growing side by side, same soil, roughly same pot size and both have flowered multiple time simultaneously and have been hand pollinated by paint brush. Only the Fwang Tung with the clear graft site has produced fruit as seen.

Now that I’m looking at my older, larger and healthier Sri Kemban, I’m not seeing any graft site even up close. Can anyone give me any input whether I have a genuine grafted tree or not?

[BloomAndSprout]

I'd guess it was an air layer or seedling then.  I'm not seeing any pictures, however.

[Aristolochia]

Sorry, pics wouldn't load right initially. They're now included. It's definitely not air layered and shouldn't be a seedling.

[Galatians522]

I don't see an obvious graft union in the picture. Sometimes a really good graft won't leave much of a scar. It would be very unusual for the tree to flower at that small size if it were not grafted.

[BloomAndSprout]

Sorry, pics wouldn't load right initially. They're now included. It's definitely not air layered and shouldn't be a seedling.

I myself have two starfruit.  A grafted Kari and a seedling-grown Sri Kemban that is 4 or 5 times larger.  Earlier this month, the Kari (smaller than yours!) produced a fruit that fell off (when I tugged up the pot I discovered and inadvertently ripped away roots had been growing in the ground, and so I repotted it) but the Sri Kemban, about as tall as a man, has not even flowered. I'd guess it's a seedling.