I grew up 100 miles north of New Orleans and love my family recipe for okra gumbo. I've also read many gumbo recipes, including several from a book called New Orleans Recipes published in 1932 by Mary Moore Bremer of Waveland, Mississippi, about 60 miles eat of New Orleans. This book explains that both okra and file powder (made from dried sassafras leaves) are thickening agents, so typcially you use one or the other. It says that the word gumbo is derived from the Choctaw Indian word "kombo," which means "sassafras." I have noticed on The Food Network Web site that famed chef Emeril Lagasse has a "Decontructed Gumbo" recipe that uses both okra and file powder.
The "Cajun" way is not the only way to make a good gumbo 'OldFrenchCajun'. I think that you are forgetting the other Southern states here that have other ways of doing it. My wife made this up for us and we love it. It's easy enough to make and has great flavor. Thanks for posting.
The person must have been a FAKE Cajun if he told you file means cooking with okra. File gumbo is never cooker with okra and Okra gumbo never has file added to it while cooking or at the table. One other thing, tomatoes are never used in REAL CAJUN FILE GUMBO. Now it is used in Okra gumbo since some tomatoes are smothered down with okra for 2 hours to make the base for the okra gumbo. Okra is never just sliced and added to gumbo.