Interesting...

I wrote the DIY that you linked above...

Step #6: Drain Exit next to jack pad: overhere I cut the leaflets a bit to prevent debris from clogging the bottom.

In any sunroof (no matter what car/model), the seal between the glass and the opening is basically a piece of felt, it is not water-tight simply bc the glass slides sideway, so the felt seal is there to keep 98% of water out.
However, there is always a 2% of water (and grime/dust from the atmosphere) that enters the channels in the sunroof cassette.

This is why it is good practice that one cleans the channel with water and some q-tips once a year, especially if one parks the car outside under the trees.
Knowing the X5 sunroff system, don't open the SR too much (lol), just a few inches to pour water in and clean it, especially the front drains...

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT