I think it's a bit more subtle than that. For one the author tells us they think this is an example of success story. Although I guess it depends on when you are measuring from, and they may be being somewhat tongue in cheek with their choice of East Germany
I think the point is that we would expect East German cities to have reasonable relative growth post-unification because we are taking a relatively structurally deprived area within a wider more successful economy.
That Manchester has kept up with areas where you'd expect to see reasonable growth, is positive. I suppose there's also the hint that this suggests that this has been allowed to happen by central government, but I could be making that up.
I think the point is that we would expect East German cities to have reasonable relative growth post-unification because we are taking a relatively structurally deprived area within a wider more successful economy.
That Manchester has kept up with areas where you'd expect to see reasonable growth, is positive. I suppose there's also the hint that this suggests that this has been allowed to happen by central government, but I could be making that up.