As described on the poem, the car's driver refers the individual who caused him to stop his car as an "old man". Therefore, it is implied the driver is much younger than that individual.
Elderly people are characterized as wise beings, given the broader amount of experience they have gained throughout their lifetime - produced by their longer primacy on Earth. Humans shape their behaviour as they age up, thus, elders think very differently than younger generations. In the case of the poem, the old man holds stronger moral values towards the toads than does the driver - creating a misunderstanding between the characters.
