I’ll bet Trump did this to cut Hillary! off at the pass from trying to announce she’d nominate Chelsea to some position.
I tend to agree. I have found that when Trump says something that sounds odd at the time, he is doing it purpose for some reason that has not yet become apparent. This very well could be the case here too.
It's illegal to appoint a member of your family to a position in government. So neither Chelsea or Ivanka can be appointed to anything.