Doesn't hurt to hook up a router and find out. But my guess is, it's turned off. You might get a link on the network port but not traffic. I can't imagine them having open access to ports... unless someone is paying for it. But then again, it's an ISP, it's possible. Try it out. Easier would be to move your work cable over and test if it just works, but since it may not you probably dont want to take down the work network. Otherwise just install a router and put a computer on it to see if it gets internet connection.
Also, yes, yellow fiber typically means single mode fiber which is meant for long distance and would be expected in this case.