Their intention is for you to provide a 50 ohm microstrip transmission line. You should ignore the 1.34 mm dimension shown for their evaluation board and design your microstrip width to suit your dielectric thickness, layer properties (like dielectric constant) and coplanar groundplane spacing. If you got .325 mm that is likely the correct one to use.
My quick calculation, assuming use of FR4, indicates that your groundplane layer is roughly .008 inches below your outer layer for that width to be 50 ohms, roughly. Is that a close guess?