Here is the standard reference picture for a hippo tusk in cross section. Normally you would see a straight line of dots appearing in an ivory piece that has been cut from lengthwise down along the left and right borders of the TIZ.
If hippo tusks indeed grow throughout the life of the animal, my guess is that your piece came from an old hippo where the continuous addition of the lamellar dentine layers over time has completely "crushed" the TIZ and reduced it to the series of dots we see from the pommel end. Notice how the angle of dots in your hilt approximately fits with the shape of the TIZ? The picture also clearly shows the laminations.
It could also just be a freak - a deviation from the norm, where an animal has been born without a prominent TIZ. I don't know - but now I'm certainly dead curious to find out!
Regarding the tea staining, I'm sorry but can't answer you. I don't know anything about it but would love to learn more! Where was it done, how exactly, how culturally widespread, since when, etc. I just know I like the color.
All the best, - Thor