None of the good barrel brands are better than the rest. LW, CZ, SR, TJ, BSA etc all have a spectrum of accuracy. The best examples of each of them are excellent and you will also find ones that are below average with every brand.
Some of it is to do with how well it is machined and fitted to the action and how well the gun is tuned for the barrel, pellet, speed, reg setting etc.
As the barrel was machined and fitted by Ernest in this case, it's no surprise that there was a noticeable increase in accuracy.