This conclusion was reached with a single experiment.
> Two teams concurrently developing the same functionality — one in C, one in Rust — are analyzed over a period of several months.
> Furthermore, Ariel OS is shown to provide an efficient and portable system runtime in Rust whose footprint is smaller than that of the state-of-the-art bare-metal C stack traditionally used in this context.
> The authors thank Davide Aliprandi and Davide Sergi of the STAIoTCraft team, and the wider Ariel OS team.
So one team had Ariel OS developer support, and it's unclear what support the other team had. Seems fair.
In Figure 12, they simply stop optimizing the code once desired rate is reached. Just at the end of the project the Rust firmware gets over a third performance boost, most likely from their OS developers.
Additionally, there is a claim that "Ariel OS is shown to provide an efficient and portable system runtime" - but there are no real tests for portability are conducted. Worst still:
> Where C-based projects require a separate project setup and manual code copying per target, Rust on Ariel OS consolidates everything within a single project [..]
This claim is just not true. This sounds like somebody that is not as familiar with C.