I Googled the submission requirements exactly as you wrote them and this is the one contest that came up. If this is the right one they responded to my request of info that it is File Size, not .jpg size they are referring to.
Trust me
I have went through everything
And I'm pretty sure the who answered your question doesn't know the difference between actual file size vs jpg size.
Anyway, I just submitted my work by resizing them in a super big size, 10k pixel by 80k pixel.
But I am sure I will write them a technical article about what just happened to me.
Thanks
Aaron
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