@JPB,
I'm guessing it is the variety of plant that was used.
Determinate varieties of tomatoes, also called "bush" tomatoes, are varieties that are bred to grow to a compact height, about 4 feet high. They stop growing when fruit sets on the bud, ripen all their crop at or near the same time (usually over a 2 week period), and then die.
Indeterminate varieties of tomatoes are also called "vining" tomatoes. They will grow and produce fruit until killed by frost and can reach heights of up to 10 feet although 6 feet is considered the norm. They will bloom, set new fruit and ripen fruit at different times throughout the growing season.
I planted both types of plants in my Albuquerque, NM garden in March. One of the early varieties is already creating fruit and should be ripe in a week or so while all the other varieties, both determinate and indeterminate are still at the blooming stage.