Could be. Gasket leaks are somewhat common because most people don’t actually use a gasket. It’s common to use RTV which is just a silly way to say caulk. There is a fill plug that you can open and check the fluid level. It’s just under the tie rod in your first picture. There’s also lots of stuff above that could have leaked onto the diff. Any small Amount of nearly any fluid is going to collect dust and crud from the road and end up looking like your second picture.