Eh, I read the article, and am a bit conflicted. The suggestion that the Celts were learning new skills in British Roman workshops, suggest that the Celts were learning the Roman technologies. In most of my studies of Celtic history and lore, I've found that the great inventions of war: chain mail, the short stabbing sword, the long sword, even the turtle formation of a unit covering themselves in their shields against missile fire are all Celtic inventions. What the Romans had was disciplined professional soldiers, and that alone gave them the advantage in war. The Roman gladius short stabbing sword was first encountered by the Romans in Spain, wielded by the Celtiberians. It took a full century to pacify Spain, after which the Romans were so impressed with the Celtiberian 'gladio' sword, that they adopted it has their primary weapon, and called it the Gladius (to make it sound more properly Roman). When Julius Caesar invaded Gaul, that was the first time Romans encountered long swords as were being produced by the Gauls. The Iranian technology of pattern welded swords had reached Gaul before Caesar arrived. So the Celts were already producing some of the best swords.
In my studies, I've discerned that the Romans didn't invent much, rather they borrowed or stole ideas from those they warred with - and primarilly from the Celts.
Too many historians in the past give too much credence to Rome and it's 'technologies'. More and more current period historians are revealing the true nature of Celts and other socalled Barbarian peoples of Europe, but there is still a core of Romano-centric historians that are too dug into their misguided beliefs.