I've got just one similar plant, Mark, and it's a 'San Marzano'.
I sowed a whole packet, and some are outside in a soil/compost, as this one is. It's not doing very well, being about 4' tall, with just one main truss, just like yours, and another just forming...
The others are all pretty well normal, so we may have a 'rogue' on our hands, or maybe a superb plant in the end - who knows!
Later on...
Just looked around and in fact we have two like that! Both seem healthy enough, if shorter...