[hesk]

The source [1] is misleading to the point of being wrong. It is perfectly valid German to say "Ich bin ein Student" meaning that one is indeed a student. "Ich bin Clown" is not grammatical at all.

[loevborg]

It's funny how (presumably) native speakers make judgments about their own language.

Of course you can say "Ich bin Clown" just as you can say "Ich bin Kaminfeger" or "Ich bin Physiotherapeut"