One of my favorite pipes, an estate Charatan dublin stack, has virtually perfect vertical straight grain all around with a noticeably darkened horizontal band around about half the bowl. I was very concerned about this when I bought the pipe and tried to find the answer to this question since the pipe was so handsome & attractively priced.
I couldn't find anything definitive, but did run across several opinions that such discoloration occurred in briar occasionally and did not affect smoking quality. The eBay description did say that the coloration was not from a burnout condition.
So, I took my chances & bought it, and today it's one of my favorite go-to pipes. It smokes well and cakes normally throughout the discolored region of the bowl, which is all I care about. I know this is not a definitive answer, but I do know that I scored a terrific pipe at a great price because of this bowl discoloration.
After receiving the pipe, I went so far as to sand the bowl down to bare wood, concentrating on the darkened area. It was indeed a condition in the wood and not something superficial.
Good luck with yours. Just watch the caking on the inside where it's darkened on the outside. If it cakes normally & evenly like the rest of the bowl, I wouldn't concern myself about it.