I don't remember the author, but Kishon and Hasek would be my prime usual suspects. (Mainly since I surely read the short story a long time ago - could be 50 years ago when I was a kid - and these two humorists I read most. Also, it was from a collection of humor stories, naturally in German - I am one.)
I don't remember the exact plot either, but somehow (surviving in journalism or so?) the author is forced to freely make up facts. Initially reluctant, he is successful with that.
The punchline is that a made-up fact about a celeb might be true after all (paraphrase by me): "Guess what, the other day I learnt that Celeb was in that town at that time after all. Now that I call creative lying."
Can you nail down the source with this flimsy data?