The idea would be, I suppose, that Edgar's midfield is a bit arse heavy, lacking a bit in terms of pure creativity: Nedved has an important role to play here as a creator of plays - and if you manage to suffocate him to a fair degree, you have done damage to Edgar's supply line, as it were.
Whether that is sound tactics or not depends, of course, on how crucial one thinks Nedved's playmaking would be in this set-up. But the idea itself isn't insane. Not in my opinion - it's a particular, tactical move based on Edgar's particular set-up - not really a reflection of Nedved's overall ability (it would indeed be absurd to single him out for a man marking job in any old set-up - but this isn't any old set-up).