What is the definition of an engineer in your eyes? In some countries there is a legal definition, so developers are not allowed to call themselves engineers unless they have an engineering degree (and not the software kind).
I just find it silly to use a definition that you typically need 4-6 years of maths heavy formal education for front end javascript that you can learn on youtube in a month.
Not in my country..
Some frontend developers are doing more actual engineering than I did when I was working as an actual electrical engineer, and I was working on buildings and shit.
Not all frontend devs, though, and certainly not the ones straight out of a bootcamp, but a lot are.
But the people building foundations for others to work on (like the target audience for this library) definitely are doing some sort of engineering.