Good morning, Michael,
I wonder if your small tomato was not one of the cocktail varieties. Thanks to the local bird life, I had a number of self-sown such plants, all bright yellow with copious yields and sweet tasting - ideal for chutney and tomato onion sauces. The plants appeared in our spring - August 2019 - and continued to bear fruit right through our winter, perhaps because my very small garden is enclosed by a high wall.
Now that we are back in this year's spring, i have uprooted these plants to make way for new veggies, but I can guarantee you that within a very short time I will find new tomato plants in every conceivable part of the garden!
Best Wishes, John