Anyone old enough to remember the show Family Affair? (3 orphan kids move from Indiana to live with their bachelor uncle in Manhattan; the uncle has a "gentleman's gentleman" Mr. French who does the cooking)
Kid is watching Mr. French make salad and asks why he is tearing the lettuce instead of cutting it with a knife, and Mr. French tells him the metal knife will bruise the lettuce, whereupon the kid asks why the salad then goes in a metal bowl, to which he has no answer.
Supposedly the metal can react with the acids in the dressing, but that would depend on the metal, and stainless steel is certainly not a problem.
American's Test Kitchen says to clean your wooden bowl in the oven:
https://www.americastestkitchen.com/articles/3959-there-is-a-reason-you-should-be-baking-your-wooden-salad-bowl