Yes. The instructor can speak in English. Perhaps, all the instructions are given in English for tourists. In case of any doubts, you can ask them and get clarified immediately. Considering millions of tourists coming from different parts of the world, the management has arranged English speaking instructors to keep them updated with the place and the activities.
It gives a sense of belongingness to the tourists and facilitates them to get closer with the inhabitants. Thus, if anyone comes from English speaking countries, they can enjoy safely without any communication gap.
However, for domestic travellers (within Thailand), the instructions are given in the Thai language to ensure that they are understood.