It's probably only that some loan companies want to see more positive "action" i.e. other loans being paid back correctly.
However, rather than take out loans to prove that you can pay them back, (not really sensible...

) I'd just apply to another loan company for the car loan: different rules apply to different companies and he might well be accepted with open arms by another company.
It's worth giving a warning though, that if he is rejected by another company, don't just keep trying others in a short space of time, because multiple applications can ring alarm bells on your report. Give it 6 months or so if another loan should be rejected.
Good luck!