How is the n100 a good choice

I don't know anything about the N100 or it's recommendations, but I think you are confusing raw cpu power vs iGPU to transcoding video. An iGPU has one purpose and that's to deal with graphics so it's more efficient and can do more with less. And that CPU has one in it so the iGPU would handle the transcodes not that passmark score.

That Plex article you are most likely looking at is looking at CPU grunt requirements for if you were to not use hardware acceleration to handle video transcoding. It was written a long time ago before hardware acceleration became dominant.

N100 can do hardware acceleration and quite a lot of it.

Intel QuickSync allows for transcoding to be offloaded to the iGPU which has dedicated hardware specifically to handle this type of processing. The N100 has plenty of performance to deal with a number of transcodes simultaneously

Tested the N100, was hardware-accelerated transcoding and tone-mapping five 4K streams with almost imperceptible delay when skipping through the timelines.

I’m not sure what you mean by 1080p streams? Do you mean transcoding from 4k to 1080p with tone mapping? Do you just mean 1080p direct streams? Regardless the numbers you are quoting is the old recommendation when doing transcoding on CPU (assuming you are referring to this 1080p (10Mbps, H.264) file: 2000 PassMark score). The n100 has intel quicksync so with plex pass you will be using hardware transcoding and thus not using the standard part of the CPU.

Like everyone else said iGPU is great on it but I still got an N305 to have it last a bit longer.

are you transcoding 10 streams? why? also, ignoring the iGPU. 

Can recommend the N305. I direct play most of my movies. This is forced transcoding to see how much resources it needed.