I have no idea what this is referring to. The first time the article mentions this (whatever this is) seems to be in the conclusions. Find the word "platform" in the article, and there is one match: in the conclusion.
I write Go on Mac or Win, deploy on Mac, Win, or Linux. One code base, one command-line option to tell the compiler which platform to target. A 2-second compile for local platform, test, it works, another 2-sec compile of same code with a different command-line option and I have a native executable for some other target platform.
I don't know what more Go would need for the "truly multiplatform codebase" that Rust purportedly allows, but I haven't used Rust. If I had to guess (again, the article doesn't seem to say), I'd guess that maybe if I were targeting something tiny, like a chip in a microwave oven or maybe WASM, Rust would be better, because you can customize the memory handling. I would certainly (learn and) use Rust over Go for such specialized cases, but then those are "specialized" cases, not general multiplatform cases. I wouldn't deploy the same code to a microwave oven and Windows.
So, I don't know. Any ideas?