The spec example

   For example, to do a 32 bit add of 0x12345678 and 0xaabbccdd, do this:
      SET [0x1000], 0x5678    ; low word
      SET [0x1001], 0x1234    ; high word

suggests he's thinking in little-endian.

I don't think it's relevant to this spec though: there's no way for a DCPU program to detect the CPU's endianness. Imagine it's C with 16-bit "char"s and no larger int sizes.