On the websocket API section that tells you how to subscribe to a trigger: https://developers.home-assistant.io/docs/api/websocket/#subscribe-to-trigger it says

For each trigger that matches, the server will send a message of type trigger. The id in the message will point at the original id of the subscribe_trigger command. Note that your variables will be different based on the used trigger.

Straight below that, there is a block of JSON that looks like a sample response... which has a type value of event. Either the response example is wrong, or the quoted statement needs rewording because it reads as contradictory. Happy to raise a PR if someone can confirm for me that I'm right.