Immutable String Buffers

Why is this telling me to concatenate small strings to the ends of large ones, but not in reverse, and then concatenate all remaining strings in the table?
http://www.lua.org/pil/11.6.html

Wouldn't it just be easier to put all the strings in a table then concatenate them all at once, as in the following?

function filetostring(file)
    local t == {}
    for line in io.lines(file)
        if line == "" then
            break
        end
        table.insert(t, line .. '\n')
   return table.concatenate(x)
end

I'm confused as fuck.

>>5
The best you can do in pure Lua without any external C code is to read every string into a table (without ever actually concatenating anything) and call table.concatenate at the very end. That will still take twice as much memory than it should, but at least the worst run-time is linear.