To Mae and Tuck, the closing incident with the toad is completely innocuous. They have no reason to think that the toad is anything other than a normal, run-of-the-mill toad. However, I believe the reader is meant to believe the toad is the same toad Winnie poured the bottle of spring water over. The reader is meant to think this because the toad is a frequent occurrence throughout the story. More importantly, Tuck's comment to Mae solidifies the fact that the toad is probably the same toad.  

"Burn fool thing must think it's going to live forever," he said to Mae.

The toad is simply sitting in the middle of the road. It is completely oblivious to the fact that there are cars and carriages on the road that might run it over and kill it. Either that, or the toad has learned over the course of about a century that it has nothing to fear from being in the middle of the road. I believe it is the latter of the two possibilities, and that the toad is Winnie's toad from earlier in the story.