IFTTT is one method of cloud integration, but not the only one. Any manufacturer which offers a way for you to send messages to their cloud may be able to accept messages from the SmartThings cloud via a custom smart app. For example, that’s how the custom nest integration works.
“Sensor tag” in this instance referred to a specific brand name. Their full name is Kao Gadgets Kumo Wireless Sensor Tag. They have a very long range. They do have an IFTTT channel, But most community members use a different cloud to cloud integration. They have multiple different kinds of sensors, including a reed sensor, a motion sensor, and a moisture sensor.