The graphic is meant to represent the top of a MacBook laptop with the requisite stickers and silver Apple logo.

Yes, yes you are. It's a shiny mac logo.

No, that’s how the shiny metallic Apple logo has always looked ever since they got rid of the backlit one. See for instance product shots of the 12’’ MacBook, which IIRC was the first: https://www.apple.com/shop/refurbished/mac/12-inch-macbook https://www.imore.com/macbook/home

I was thinking dark mode.

Or the silver/black split could represent their consumer/professional split, as in the color of the Apple stickers and keyboard/mouse that come with the consumer/professional Macintoshes.

You really can't accurately guess what the symbolism in Apple's WWDC banners might mean. It's intentionally too vague to decode.