Could be unintentional aswell. Lots of trees have a very sturdy root that is resistant to lots of pests and can survive in most conditions. On top of that they graft a pretty part that usually doesnt grow to tall. Sometimes though the root part grows partly through the top part of the tree and you get a result like this. To say for sure what it is you need to wait until they cut the tree again because the branches from the root part would be much larger than the intentionally grafted ones.