This is more like a tutorial than a product though, with code examples in Rust. "How to write an android emulator from scratch in C" would appeal to a slightly different audience.

I'm finding all the bellyaching about people saying X was written in rust a lot more annoying than what's being complained about.

But then this comment is 3rd-order bellyaching so feel free to downvote it.

Depends, sure it's not the main quality of a software. But it can also hint at some potential features of the language (unless proven wrong) : Speed, safety, potential interest for longer term. You can have ultra lean software written in Java, ultra fast written in Python or simple to understand / develop to written in Rust or C, modern written in C++98, but it's generally the other way around. So, it's not the first thing to mention when speaking about a program, but interesting nonetheless, an element of context.

It should be obvious from even just the headline that this is not a real product but instead an article about how to implement an emulator, and for such articles the language is very relevant. Or do you also think that being the worst is another feature?

Features are something that matter for products, which this isn't.

This just seems like a project that someone wrote and decided to share with the world, and show how it works with full source code. In that instance, the fact it is written in rust is relevant because, as noted in the first paragraph, the reader is expected to have a working knowledge of Rust.

Depends, some time it does matter when security and performance are part of the non-functional requirements, validated on project acceptance delivery.

Marketting is not mostly about features.

What if that something is a library?

It is, if you have an advertising budget.