No difference (Score 1)

The way I've seen this approached is that, if it's a good interview setup you are not the only one interviewing him and there is reasonable coverage with people who can interview on that level.

So interview him as you would someone on your level, this will atleast give coverage on deeper issues they may not get with 'higher ups'

Also you could think of an issue that you personally had trouble with and ask them about that. How they answer it should give you some idea of if they are in fact above your level.