They sell a lot of trucks, if you add gmc and chevy for and gm are very close. Ram is a somewhat distant third.
Does it make Ford the best, not really. But it does mean that more people chose to spend their money on a Ford so they thought it was the best choice for them.
My personal truck is a Chevy (but would also have gotten a ford if the deal was right), my work truck is a Ford. They are both decent vehicles. I have few complaints for either. I don't know what my next truck is going to be. I like the Ram trucks a lot but I don't know if I am sold on Chrysler's quality yet. If I had as much faith in Ram quality as in Chevy and Ford my next truck would probably be a Ram.