I would hope he is not using LMR-400. It's far to UN-flexible for snaking through most mobile installations.
Having said that.... He probably DOES mean RG-400.
(RG-400/u) which is a Mil-Spec coaxial cable. Dual shield, silver plated inner and outer conductors, with a Teflon dielectric. PASTERNAK has the complete data SPEC. SHEET here:http://www.pasternack.com/pdf/RG400U.pdf
Don't be too quick to "jump" on someone's statement as incorrect, sometimes they DO INDEED know where-of they speak.