Either the HOG operation was looking shaky and it was shut down, or the HOG was working together with the EOG. I am inclined towards the former but the latter could also be possible from the sound of the EOG.
Even if there is no explicit failure in the equipment, the HOG operation is tricky enough that there can be glitches in the power supply while passing through neutral zones, or a bad power factor due to improper load on the HOG system. In such cases, it would not be advisable to run the HOG system and the train will be put of EOG (The Mumbai Raj was experiencing that in the initial days of it's conversion to HOG. Because of issues...
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with neutral zones, the train had to be run with EOG cars).
However, it could be that both were operational if the HOG system was not able to take the load. Each EOG can contains 2 generators. And normally, each generator is connected to one of the two feeders running along the length of the train ( the two large cables connected on either side of the coach). Both generators cannot be connected together, so each one powers one of the feeders (or one can power both feeders, like a HOG loco). During normal operations, one generator in each EOG car is powered and connected to the feeder ( Technically, one single EOG car is enough to power any of the trains running on IR, even the longest fully A/C trains. Two cars are used for efficiency and redundancy). In the video, it seems that the sound from the rear EOG is quite low, so probably only one of the two generators was running. In that case, the the other feeder line has to be powered from the front EOG or the HOG system. But I am not sure if such kind of operations are cleared in IR right now. Documents for HOG operations are not readily available as the system has started only recently.