[yzydserd]

In another article at https://www.bbc.co.uk/future/article/20230302-the-giant-arcs...

“According to Lopez's article, it is extremely unlikely (a probability of just 0.0003 per cent) that such a large structurei could have arisen by chance.”

The particles to make up the structure had to come from somewhere, and the best models of gravitational movement would say that such a structure would have taken too long to form. The arc is 1/15th the radius of the known universe.

Such a structure isn’t ruled out by the cosmological constant. It’s highly unlikely.

The distinction here is “unlikely to form anywhere” versus “unlikely for us to be situated in a position we could see such an unusual formation”.