It may be a trick of the eye by the fact MPX boards are large, but here's a Sapphire RX 580 for reference:

Based on the position of both those connectors I would beg to guess the power delivery and most of the control circuitry for the display ports are on the motherboard.

If that sounds accurate it's beyond me why any manufacturer would do that. But I mean, hey it's Apple, "Think different!" am I right?

But then again it kind of makes sense. They wouldn't want you plugging their GPU in another vendors board. Best way of doing that, don't put all the components on the card.

@Windows7ge I think you're right. The two chips marked yellow are DP to HDMI converters and the card only has HDMI outputs.

A few DP connections are probably being routed back to the MPX slot to feed the Thunderbolt controllers.