can only think of two reasons why this would occur
-hair is near the end of its natural growth cycle, its chucking out the last few molecules it can and naturally tapers off in diameter before it goes into resting phase
-hair is miniaturising due to DHT at a rate aggressive enough that it occurs within just a few cm's of growth
Yes, this is a sign of balding, but depending on your hair it could be a false flag. Some people have hairs that lose color at the base, and the absence of color makes the root look thinner than it actually is.