If he bought back green coffee then expect "Border Security" and DAFF (formally AQIS / Customs) to kick your door in followed by a TV crew as green Kopi Luwak is still illegal in Australia.
If it was roasted then you are allowed to bring back less than a kilo and I would expect:
An unknown roast date.
and hopefully not from a caged Luwak
Finding "real" Kopi Luwak is pretty hard, most of it is either fake or from cage fed critters.
I would suggest roasting-up some of that Sumatran next week and doing a blind taste test of the two coffees side by side. I bet I know which one is better.
Upside is that you will be able to say you have tried it and will know you don't need to ever again and hey... it was nice that your brother thought of you while on holiday too