It would be called...something else is pulling on the rubber band, and the rubber band is not "eccentrically contracting" itself. The resulting "tension" was put onto or into the rubber band by something else.
But the bigger question is...do you believe that muscles are like rubber bands in how they work?
They contain some elastic properties but if I am being honest I don't know if I would say they work like rubber bands or not. Muscles can be contracted rubber bands are in a constant state of contraction while at rest. So I guess my answer is in some ways they do work like rubber bands and other ways they don't.
My question for you is, do you think Fascia is stuck to the muscle that it surrounds?