"French" refers to the manner/style in which the potatoes are cut....they are "frenched" or sliced squarely and thinly. The English call them "chips" because the potato pieces are chipped off (large chunks).
Potatoes were first introduced to Europe not through the French or Belgians, but through the Spanish. In 1537, Jimenez de Quesada and his Spanish forces encountered a village in Columbia where all the natives had fled. Among other things, they found in the native’s food stuffs potatoes, which the Spanish initially called “truffles”.