Hi there,
short term loudness of -18 LUFS, is only required for programmes up to 3 minutes lenght, which I believe is not your case. It makes part of the suplement 1, of the EBU loudness specs , in this case R128.
For programmes longer than that, -23 lufs integrated and maximum peak of -1 dbtp are the only requisites for broadcast material. If your client is asking that for a DVD release without mentioning short term, thatīs the explanation.
You can find more info on this EBU doc here:
https://tech.ebu.ch/docs/r/r128s1.pdf