Hi! I have done something similar to you for my motion processing. I have also used 000021 as the example motion similar to humanml3d. The raw offset is the general direction of the joint from the parent. However, if you visualize the motion (as shown below) you can see that the relative offset of the first finger joint is at -1 y from the wrist similar to lines 94 - 99 for t2m_raw_body_offsets. While finger joints 2 and 3 are on the x-axis. However you have the raw offsets of all finger joints on the x-axis, denoting the fingers are pointing in the x-axis for 000021. Can you recheck again?
This is what I have:
p - pinky, r - ring, m - middle, i - index, t - thumb
left hand
[0, -1, 0], # lp1
[-1, 0, 0], # lp1
[-1, 0, 0], # lp1
[0, -1, 0], # lr1
[-1, 0, 0], # lr1
[-1, 0, 0], # lr1
[0, -1, 0], # lm1
[-1, 0, 0], # lm1
[-1, 0, 0], # lm1
[0, -1, 0], # li1
[-1, 0, 0], # li1
[-1, 0, 0], # li1
[0, -1, 0], # lt1
[0, -1, 0], # lt1
[0, -1, 0], # lt1
right hand
[0, -1, 0], # rp1
[1, 0, 0], # rp1
[1, 0, 0], # rp1
[0, -1, 0], # rr1
[1, 0, 0], # rr1
[1, 0, 0], # rr1
[0, -1, 0], # rm1
[1, 0, 0], # rm1
[1, 0, 0], # rm1
[0, -1, 0], # ri1
[1, 0, 0], # ri1
[1, 0, 0], # ri1
[0, -1, 0], # rt1
[0, -1, 0], # rt1
[0, -1, 0], # rt1