This algorithm is O(n^2) in classic OO languages too!

I think what this is is a translation of a classic OO "array.add(x)", which would usually be O(1), into "array = array + x", because that's the closest you can get in this language. However, mapping that translation back into a language you know, that should raise alarm bells, because it looks like it should be O(n) and allocate garbage like mad.

So, rather, i think this is classic insufficient paranoia and self-doubt when doing an unfamiliar new thing.

It totally is. Learning!