Understanding traffic graphs

[bubbagump]

See my screenshot here: https://imgur.com/a/GfhtIB0

The question is why don't the two graphs correlate? If one looks at 10:40:55 you see there is a top talker using 4Mb yet the aggregate graph at the top shows only 620Kb. This makes no sense to me. I would expect the top aggregate graph to be at least 4Mb and likely more when considering other hosts talking at this same time over and above the top talker.