I grow runner beans in various beds and in containers. In my experience it's very normal for plants in different locations, and even plants in the same container, to grow at different rates.
Not all seeds germinate at the same time - you can have a difference of many days between one seed and another. So genetically your seeds aren't all identical. There can be slight variations in the soil, micro climate etc. For example, with my peas this year (which were outdoors in containers when it was still really quite cold) did better one one side of the container where the lip of the container gave the small plants protection from the prevailing wind.
I have several squash plants that all germinated the same day and grew at exactly the same rate when kept indoors in pots. But once planted out some have romped away and are a few feet long, whereas others have barely grown since planted. This happened last year too, but the slow starters turned out to be the biggest, most productive plants.
I have hundreds of beans of various type growing in my garden. Some are already at the top of 8 foot bamboo canes and others haven't yet found the cane to wrap around it. Same variety, same conditions, same location.
However, it doesn't follow that those that are vigerous early on will produce the biggest crop. Like kids - they have growth spurts at differing times.