The evolution of RFID-based passive Internet of Things (IoT) systems comprises three stages: traditional UHF RFID (also referred to as standalone or Passive 1.0), local area network-based coverage (networked or Passive 2.0), and wide-area cellular coverage (cellular or Passive 3.0). Wireless sensing in passive IoT is characterized by zero power consumption, low cost, and ease of deployment, enabling object tagging and close-proximity sensing. With the emergence of cellular passive IoT, passive IoT wireless sensing is playing an increasingly important role in enabling ubiquitous sensing within IoT systems. This study first introduces the concept and development path of passive IoT. Based on fundamental sensing principles, recent research advancements are reviewed across four representative objectives: localization and tracking, object status detection, human behavior recognition, and vital sign monitoring. Given that most existing research relies on commercial UHF RFID devices to extract signal features for data processing, the development direction of passive IoT wireless sensing technology is further examined from the perspectives of new architecture, new air interface, and new capabilities. Moreover, this study offers reflections on the integration of communication and sensing in the design of next-generation air interfaces from a sensing-oriented perspective, aiming to provide new insights into the advancements in passive IoT wireless sensing technologies.