I was re-reading the Bitcoin white paper, and found this paragraph relevant for us here here:
Nodes always consider the longest chain to be the correct one and will keep working on
extending it. If two nodes broadcast different versions of the next block simultaneously, some
nodes may receive one or the other first. In that case, they work on the first one they received,
but save the other branch in case it becomes longer. The tie will be broken when the next proof-
of-work is found and one branch becomes longer; the nodes that were working on the other
branch will then switch to the longer one.