Does this look like graft?

Plant is a Yuzu Tree

The tree is declared as a "Citrus Ichangensis x Citrus reticula" but the buldge looks suspiciously like something after a grafting process.
I don't have a problem with it but the seller didn't mention any grafting being done.
I am also cautious because I live in a zone 7a area and don't wanna kill my first attempt.

Any help is appreciated :)

More pictures: