Plant branching off.

Self topping. Happens sometimes. Nice it did this on its own on an auto flower. now you can LST like its been topped but it was not giving any HST so it won't strss it out to much.. Good Luck!

Although not common, it is not that uncommon either, I have seen this quite a few times over the last 40 years of cultivation. Sometimes plants/branches do this for no apparent reason, it is just a slightly weird genetic mutation. It is nothing to be worried about or panic over and it is exactly the same as if the plant has "topped" itself. I have seen both main stems and any number of random branches do this on various plants, it does not seem strain related, caused by damge or poor nutrition etc, just a random mutation that won't affect potency negatively, but will increase yields positively.

Branches dont just break off it can be the lst training,put something there to support the breaking branches like a grow net for support