That discussion must have been really long ago, otherwise you missed the point. Since Lua 5.0 (2003) tables are implemented as a pair of an array and a hashmap,

That discussion must have been really long ago, otherwise you missed the point. Since Lua 5.0 (2003) tables are implemented as a pair of an array and a hashmap, and the array part can even handle small nil gaps. So tables used as arrays are implemented as arrays as well.