It's actually an inflorescence (flower stock) and not a runner. Amazon Swords can do this while submerged a couple times a year but actual flowering depends on the exact species of Echinodorus. The flowers are actually one of the only ways to identify the exact species of sword as even with the same species the leaves are known to take on different sizes and shapes in different people's aquariums.
But, yes, new sword plants will grow on the nodes of the inflorescence and, if you want, you can save them to create all new plants. It should be fine in a 55 gallon. They leaves will probably never break the surface.