It is a little confusing how they name things. DDR4 used 16b "channels" too. But that was referring to the DRAM chips themselves. What we traditionally think of as a memory channel is referring to the DIMM package itself. If you take 4 16-bit chips and put them on a single DIMM package, you get a 64-bit channel.
I mean, you aren't technically wrong, though DDR4 chips comes from x4 to x16. But that's more about it in desktop for DIMMs really.
If you per example take at other places you will see it that it's different, per example Renoir supports quad-channel LPDDR4 and it says so explicitly in the Linux kernel
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Four channels with each having 32 bits(actually 2x16) for 128 bits in total.
The difference is that in the case of DIMMs, it's putting those DDR4 chips into a topology such as that they act like a single channel, which is what we normally know DDR4 as for.
I believe that the most common in mobile and in those other applications it's really to just not tie them together like in DIMMs, unless you don't can't support that many memory controllers. Which honestly, there's no really no reason to not if you can.
If you look per example at this, it's show a package solution for it and overall it's better and more performant to do it using 4 channels(4x16 bits memory controller) than to tie them into a single channel(so 64 bits memory controller). Though at this point, who the fucks knows. I would certainly hope for a full 128 bits bus though.
