Hi Natalie!

That appears to be natural. You might want to check the origin of the branch and look closely to see if you can distinguish a 'branch collar,' as pictured at this link: https://www.researchgate.net/figure/The-branch-collar-and-bark-ridge-are-very-apparent-on-this-northern-red-oak-The-branch_fig3_237776480

I'm often amazed how a portion of a tree is able to be 'absorbed' by the trunk or even another tree! Trees produce new xylem and phloem tissue each year (these make up the rings) causing the tree to increase in diameter and grow around anything in it's way. A quick internet search for "trees that grew around things" results in some pretty interesting sights. 

With hopes this helps. If you have any additional questions, please feel free to reach out. 

Thank you,

Julie