I am a professor at an academic institution in applied mathematics. Last year around summer, a Masters student in my research group wanted to switch from his supervisor towards my research interests as he became more interested in my line of work. He displayed enthusiasm during my classes with advanced, interesting questions and by coming to my office hours before mentioning that he would like to switch.
After having an extensive discussion with his supervisor, I decided to take on the student's supervision responsibilities. My student worked well on his research for the first two to three months. Given his level of enthusiasm, I expected him to continue on for a PhD with me. So, I was quite surprised when he mentioned that he wanted to end with just a Masters and not continue on to a PhD. He mentioned that he did not know what he would like to do after his Masters, and that he would just like to focus on writing a good Masters thesis for now.
Since then, I had the impression that he has not been putting in enough work every week. His work has been alright and okay and sometimes mediocre. I had the impression that he might have been working on somethings totally different which is not related to my line of work.
Wondering about his interests to guide him in the right direction, I plan to ask him about his future plans and to ask him to just write an okay thesis and put time in to work toward his future goals, be it a job or further studies. Is this the right thing to do as a supervisor? Is the student being ethical here?