Yes, but I am going to assume that I know the definitions of those two that your instructor is working under. Ecotourism is simply tourism with an ecological attraction to it. Just because I give boat tours in the Amazon doesn't mean that I am doing so sustainably. Sustainable tourism, on the other hand, minimizes the footprint it leaves behind in the environment in such a way that the tourism could extend indefinitely, hand in hand with the species and habitat it operates around and within. Keeping the distinction, or adding the level of labeling to these two kinds of tourism allows those of us who want to be "green" tourists to tell the difference when we book our travel.
Sustainable tourism and ecotourism two different type of tourism. This difference between them is neither useful or useless. the difference just exists. Eco tourism refers to responsible tourism to places with some attractive natural attractions that have not been damaged or otherwise altered significantly by human activity. here responsible tourism means that the tourist activity does not damage the tourism destination. The purpose of ecotourism is to expose interested persons to various natural environments and features, and to promote the cause of environmental protection.
Sustainable tourism, on the other hand, refers to tourism activities carried out in a way that does not so alter the basic character of a tourist destination making it, in the long run, unfit or unattractive as a tourist destination. Sustainable tourism may involve concern for preserving and protecting the natural features of a tourist destination, but that is not its objective. Objective of sustainable tourism is to ensure continued attractiveness of a tourist destination, and therefore its utility as a tourist destination. To achieve this purpose, sustainable tourism may involve some deliberate alteration to the natural environment.