Without knowing what software they're using, that does sound pretty typical for rendering video. Presumably the size of the footage on disk is bigger than the available RAM, so it's being loaded into memory continually to stay ahead of the CPU. Towards the end of the job you should see the RAM usage decrease as the last of the stored video is pushed through the renderer.
If they want to perform other tasks while rendering, there should be a "memory usage limit" setting in the video editor that will leave some RAM free for other applications.
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