[details=“English Translation”]I heard that he passed the exam.[/details]Why habe not hat?
Because it’s hearsay?
I hadn’t noticed this use of habe until you mentioned it @danielportersax. As @morbrorper alludes, it’s probably is because the speaker has doubts about the veracity of the statement (i.e. indirect speech: I heard someone say this thing - I don’t know if it’s true or not), which is expressed like so:
Yes, I had a feeling too that it’s subjunctive.
As an anecdote, for French learners, when it is used, subjunctive also often translates uncertainty (eg: “Je crains qu’il ne soit malade”, I fear he might be ill - but it isn’t certain.)