They start with thicker items as these are least likely to "leak" down Into your lungs. Thinner liquids easily run down the path of least resistance into the lungs, especially if you dont have an epiglottis. The Epiglottis is what closes to protect the lungs from food and fluids. I imagine this will be quite a feat to swallow and not aspirate. Perhaps the SLT has some swallowing techniques to teach you to prevent this from happening. I hope this goes well for you and that you are able to restart swallowing.
Tammy