You could. But you need a large enough volume to really separate the trub and yeast. If you used the same large jar and only two pint jars, you would get half the yeast.
But he only wants half the yeast. He'll get the same amount of yeast in each jar as he would have if he filled four jars, and in this thread it's generally been agreed that the yeast collected in one pint jar is a good amount to use to pitch into a starter.
And he thinks he only brews often enough to use a couple of these saved yeast jars before they go bad. So he can just do the rinse in the carboy, the rinse in the big container, and then fill two jars and toss the rest.