That was a remarkable quote for it shows Twain’s practical side as well as his humorous side; however, since he likely got paid for the piece as a whole, he has to admit that he just did what he claimed to avoid.
Paying by the word encourages verbosity.
Wit demands brevity.
I doubt they paid by the minute.
Besides his point was he got paid seven cents for short words, same as long ones. He wouldn't use some big words even if he got paid by the letter.
Rereading my post, Twain said it much better.