neither, they didn't measure anything

they compared the Ubuntu minimal recommended RAM to Windows absolute minimal RAM requirements.

but Windows has monetary incentives (related to vendors) to say they support 4GiB of RAM even if windows runs very shitty on it, on the other had Ubuntu is incentivized to provider a more realistic minimum for convenient usage

I mean taking a step back all common modern browsers under common usage can easily use multiple GiB of memory and that is outside of the control of the OS vendor. (1)

As consequence IMHO recommending anything below 6 GiB is just irresponsible (iff a modern browser is used) _not matter what OS you use_.

---

(1): If there is no memory pressure (i.e. caches doesn't get evicted that fast, larger video buffers are used, no fast tab archiving etc.) then having YT playing likely will consume around ~600-800 MiB.(Be aware that this is not just JS memory usage but the whole usage across JS, images, video, html+css engine etc. For comparison web mail like proton or gmail is often roughly around 300MiB, Spotify interestingly "just" around 200MiB, and HN around 55MiB.