You are correct that 1-based indexing is the norm among mathematicians, but none of the creators of Lua is a mathematician, AFAIK. You can read about the early history of Lua here:

https://www.lua.org/history.html

And a lot of the time it makes the syntax more compact than it would be with 0-indexing.

  for i=1,#arr do
    foo(arr[i])
  end

I don't feel that strongly for or against either way of indexing though, they both have their pros and cons.

> The 1 indexes are only a difference from what you're used to

The left handed scissors are only a difference from what you're used to.

> Lua was made by mathematicians

The default value is nil and using nil as an index on a table returns nil. Yet nil + number is not valid and results in a runtime error.

> it's pretty much just a leftover habit from C devs

It's reflective of the fact that these languages are either intended to work with C APIs or are implemented in C itself. This makes writing FFI and extensions _far_ easier than it would be otherwise.