zahavasdad,
DaasYochid answered a lot better than I could have. There must have been an assumption that something like iceberg lettuce would be used (not romaine or other greens), and cross contamination like what Syag Lchochma pointed out would be avoided. Dressing would also be an issue, as well as other common salad additives like crutons, hard boiled eggs, etc. Also, did your rav give you this psak just for the circumstance of your first day on the job business dinner, or did he say eating salads in non-kosher restaurants could be your modis operandi?