my best guess is that the first frame of the match counts as frame "1" for the invisible timer. this means that the start frame, 450, is counted as dqframe 1 in the 20-frame sequence. this would then make frame 431 frame "20", followed by 430 resetting it back to "1".
(this part is actually incorrect, it's just a coincidence that your first contact was on a frame that ended with 0 lol)

if this is true, your elbow touches at 370 (timer has just reset). the game could've kept checking for frames to DQ on in that 20-frame period between 370-350. when your elbow contacts again at 354, there might be a gap that gets filled (370 - 354, game believes 17 dqtimer frames have passed). that contact continues until 351 when you are DQ'ed, so 20 frames have elapsed since first contact.

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i also disproved my first theory of there being a "frame total" that the game checks for. in the replay below, i contact my elbow with the ground more than enough times to get over 20 frames, but i'm not DQ'ed until frame 113. interestingly enough, my last elbow contact before being held down to DQ was 132.

if the last dqtimer reset took place on that frame, then that could mean the game checks between each 20-frame gap (with frame 1 being the first joint contact with the ground) to see if any new contact has taken place yet. if not, it forgets the "first" contact frame and looks for a new one. in this case, it had been a while since that contact at 132. the game looked at the following 19 frames after 132 (as 132 is frame "1") to find a new contact and managed to find some instances that lined up. this results in the 20-frame (technically 19) difference that DQ'd me.