Virus or burn or normal?

[Troythediver]

I noticed this black spot on the base of a new growth for my potinara. There are no other black spots that I can see. The leaves all look healthy and I am wondering if what I am seeing is normal. I water it every 7-10 days. What does the group think it is? Virus, burn, or something else. It is also currently growing new roots on the next oldest growth. They have an oddly pitted appearance.

I should also mention that the window was blocked for about three days while my house was being painted. Is it possible that when the sun hit it afterward that it was too much of a shock on this growth?