Your distinction between liquids and smoothies is problematic. How do you define either of them? There are countless complete meal replacement drinks (e.g. Soylent, as someone already mentioned) that are definitely liquids, and arguably smoothies. But they are also arguably not smoothies, depending on your definition. The one I use is primarily milk protein isolate + vitamins and heavy cream. It tastes like a thick milkshake. Does that count as a smoothie?
Your distinction between liquids and smoothies is problematic. How do you define either of them? There are countless complete meal replacement drinks (e.g. Soylent, as someone already mentioned) that are definitely liquids, and arguably smoothies. But they are also arguably not smoothies, depending on your definition. The one I use is primarily milk protein isolate + vitamins and heavy cream. It tastes like a thick milkshake. Does that count as a smoothie?