I think he was probably referring to the 2016 iPhone SE. Many people who put priority on size are still holding on to 2016 iPhone SE since it is the only reasonably capable phone that is that small (iOS or Android)

Dimensions:
2016 iPhone SE - 123 x 58 x 7.6 mm
iPhone 12 Mini - 131.5 x 64.2 x 7.4 mm
2020 iPhone SE - 138 x 67 x 7.3 mm

There are some who do use rust for microcontrollers. Rust's defaults unfortunately do make for large binary sizes, but there are things that can be done to get similar sized binaries to C. Rust does need to make them more accessible, though.

From the rust FAQ: https://www.rust-lang.org/en-US/faq.html#why-do-rust-programs-have-larger-binary-sizes-than-C-programs

This is older and unofficial but still informative: https://lifthrasiir.github.io/rustlog/why-is-a-rust-executable-large.html