So salad fork?

And to be honest I switched from salad fork to entree fork about half way through my meal just because the question was bugging me

It matters not whether the salad is the main course.

Regardless of size, if a salad is not the main course then don't use the entree fork. Reserve the "entree fork" for the main course, whatever it might be.

In particular, side salads / appetizer salads should be cut or torn small enough in the kitchen so they can be eaten with a fork and no knife.

Ideally there is an appetizer fork, a main course fork, and a desert fork at the place setting.

if it's an appetizer salad, then salad fork. If it's an entree salad, use the entree fork. Makes sense, thanks.

Salad forks have shorter tines. You might be sticking an entree fork into a thick filet, but unless the salad contains thick chunks of tomatoes, too thick for the salad tines to pierce fully, use the salad fork. If necessary use or switch to the longer tines for thick morsels.

Simple and practical, and how etiquette evolved.

This is getting too deep into my thought process but was thinking that if I had ordered a steak salad I would have immediately grabbed the entree fork But since my nicoise had thin slices of tuna I started using salad fork.

...then eat the rabbit.

But then, I'm a carnivore--I didn't claw to the top of the food chain to eat lettuce....... YMMV.

Since your meal was one course, the salad fork should have been removed when you ordered salad as your one course.

But nobody cares about these early 20th century rules that were invented by selfish rich people who wanted to be mean to others!

Use the fork you like.

I remember that being done fir me in higher end restaurants and didn't think twice about it. Yesterday's restaurant was a nice college town restaurant but not super fancy though everyone was dressed up for graduations.