What can be the causes for this? Faulty tube seems like the obvious one.
Sure, but not likely to be a manufacturing fault, IMO.
Might a kink in the tube at install time encouraged something like this?
Yes, but if your tire size is within the suggested range for the tube, then I wouldn't think so. Unless maybe it got twisted somehow while installing. I liberally powder my tubes and tire so that they will not stick to each other and will move into the proper position when inflated. I even deflate and re-inflate them several times after changing tire and/or tube in hope that will let them find their proper orientation with out twist or uneven stretching or other such.
Could this be an indicator of the tire being ready to replace?
Could be, but not without additional evidence the tire is bad.