From the limited exposure I have, it seems to be inconsistent terminology. Some treat the postabsorptive state as a transition period between the fed state and the fasted state, but some seem to consider anything after the fed state (absorptive) to be post-absorptive – which, to be fair, is the literal interpretation of the word.
Once food has been ingested, it has to be digested, and then the nutrients must be absorbed into the blood stream. That can take up to 4 hrs for most people. So, “postabsorptive” refers to the time after “active” absorption. In this sense, the term is synonymous with “fasted.” However, in practice, when people talk about fasting, it usually refers to the period beginning after the last meal was completed, which could include the absorptive phase. That’s why hormonal changes associated with fasting occur within a time-range. For all practical purposes, it doesn’t matter. The literature uses more specific terminology as part of research: answering questions, collecting and analysing data, interpreting results to plan or inform next steps.