Did they tell him why the visa was rejected? I know that authorities in Gulf countries usually don’t tell you the reason for a visa rejection, but sometimes you might be lucky to find a nice person there, who actually does his job and informs you properly.
One of my colleagues (Pakistani national, been to Kuwait dozens of times) had his Kuwait visa rejected, because his passport was due to expire in 5 months and 2 weeks. And the rule is, that the passport has to be valid for at least another 6 months. In his case at least they told him the reason, so even though he couldn’t attend the meeting he was supposed to go to, at least he knew what to do to avoid this for the future.