That would be very odd indeed, if true. Anything Japanese is referred as yiipun in Thai or Jare-pair-nis in English by Thai people. Jap is a derogatory contraction that is mostly used by farangs (Americans especially?). I could be wrong but his name could be a poor or simply convenient shortened version of the very common Thai name Jeap ("chee-yup") as a result of years of farang mispronunciation.