I have a question about a very interesting situation. A friend of mine was working as a student worker and was offered additional pay by a student that was supervising him to create figures/maps for what, at the time, appeared to be simply for work purposes. My friend now recently discovered the work he did was in that student's PhD with only a general acknowledgement of my friend, not of his specific work. His methods do not mention that the figures were created by my friend and the figures do not cite him either. Is this a form of plagiarism?