That is a Brace Ric, for strengthening the chassis. Do you have one fitted, but I doubt it would be an MOT item for inspection anyway...
Maybe they are confused, and are talking about , Why not take the car back and get them to show you what they are talking about?
http://www.courtesyparts.com/551a0-link ... 15822.html
Or,
http://www.courtesyparts.com/55110u-rod ... 15821.html
Or,
http://www.courtesyparts.com/kb_search_ ... ?keywords=[56261N]+\(z33&cPath=714_715_800_804
You should be looking for something that looks like this, if they are talking about tie-rods.
http://www.nengun.com/tein/strengthened-tie-rods
Another good site that gives exploded views.
http://www.courtesyparts.com/350z-parts ... 0_804.html