Really the Vikings were the copycats truth be told. They were just doing the same thing that people on the periphery of the Roman economic/political world had been doing for centuries.

Dating back to the time of Alexander the Great, the Mediterranean world and the rich economy that it nurtured encouraged the involvement of outside parties. Since before Augustus was a glimmer in his father's eye or Varrus was leading troops into dark forests, there were peoples from North Sea world and the broader world of "Germania" that sought to exploit the wealth of Mediterranean polities. Viking raids were just an extension of this phenomenon. As the German lands of the former Germania developed and became a part of the broader Mediterranean/Riparian world the "frontier" of raiders and traders shifted as it had for centuries, the Norse were simply the last people to be able to take advantage of it by virtue of their geographic isolation.

Indeed they were hardly unique in most aspects of their life. You specifically mention longships as if they were some sort of uniquely Scandinavian ship, when ships similar in construction to them have been reconstructed from England. The Sutton Hoo ship as a part of the burial for example bears striking similarity to the long ships of the Norse, though it lacked a central mast and it is not clear if it was capable of sailing. Similar ships were used across the North Sea world in England, the Low Countries, and southern Scandinavia, they were not a unique Norse feature. The Norse may have pioneered certain developments, such as the use of more advanced sails, but the design of the ship was commonly found around Northern Europe long before the "Viking" Age started.

Now it is worth mentioning that the English did try and build their own fleets in response to the Norse threat, which varied in efficacy. It is worth mentioning that sources such as Alfred the Great's biographer, Asser, mention that the English did capture Norse ships and it is not outside the realm of possibility that any technological gap between the Norse and English or French was quickly neutralized in ship building based off of these captured ships, assuming that any gaps did in fact exist.