I have always pushed the bushing into the arm first. Only because I found it easier to support the inner sleeve with a properly sized 1/2" drive socket while pushing the shaft into it than it was to reach around the shaft to push on the outer shell.

But which ever way the installer finds easiest will work. As long as the inner shell is properly supported during the push.

And we had always used Moog suspension parts. Until the last few years. Now they are CRAP! What a shame.