This is not a tense but a grammatical mood, it's called the inferential mood. A bunch of languages have it to distinguish eyewitness accounts from reported speech.
Verb tense has to do with an action's relationship to time, mood expresses the speaker's relationship and attitude to the action. English is pretty low on moods (indicative, imperative, subjunctive), while other languages have a more fun arsenal.
https://en.wikipedia.org/wiki/Inferential_mood
Verb tense has to do with an action's relationship to time, mood expresses the speaker's relationship and attitude to the action. English is pretty low on moods (indicative, imperative, subjunctive), while other languages have a more fun arsenal.