The behaviour was defined this way in the original post, you may want to go check it out.

the strings might end up being attatched so add a space everytime you add to the string

Oh cool, I didn't know about that constructructor for StringBuilder. Thanks!

Oh alright, interesting. Thank you!

you've been taught right. But for simple loops, the compiler can effectively optimize them and replace the += stuff with the equivalent of a StringBuilder, giving you the same performances. Tho, don't use that with more complex loops, because then you're mostly "relying on luck" about the choices the compiler does.

Did += get faster? I remember being taught that += is really slow because it has to rebuild the strings, but I could be misremembering