NotIn order for something to constitute a clause, it is required to have a finite form of a verb. As there are a lot of scenarios where there is a comma, but not two finite verbs, not every comma creates a subordinate(subordinate) clause. Here are just a few constructions with a comma and no subordinate clause, this is not necessarily a complete list:
- Some commas are just enumerations:
Ich gehe zum Bäcker, nach Hause, und danach ins Büro.
- Another common counterexample of your hypothesis is a paratactic structure, that is two main clauses connected by a conjunction. Conjunctions of und, oder, and denn, (and others probably, this is just off the top of my head) combine two main clauses:
Ich gehe zum Bäcker und danach gehe ich nach Hause.
Ich gehe zum Bäcker oder ich gehe ins Büro.
Ich gehe zum Bäcker, denn ich habe Hunger.
There is a lot more on this, and I recommend you read a grammar introduction into main clauses and subordinate clauses in German. Maybe [this]1 could be a good start.
- A third example is an apposition:
Monika Meyer, unsere Direktorin, ist heute im Urlaub.
- Another group (and this is the one in your example), is just an interjection:
Ja, du hast das wohl gemacht.
[Ja,] cannot be a clause, because it has no finite verb.