Question about citing bachelor thesis?

You've basically understood primary and secondary sources correctly. However, if your academic journal has any lines of thought based on the cited primary sources, but which aren't actually included in the primary source, then the journal is the primary source for that line of thought. And you should always cite only the primary source, if possible.

An example (for illustration purposes only):

Primary Source 1 is a behavioral study with German Shepherds, with result X for German Shepherds. Primary Source 2 is a behavioral study with Chihuahuas with the same result X, but for Chihuahuas. The scientific journal cites both and states: "Since both behavioral studies produced the same result, it is reasonable to assume that the result is independent of the dog breed." This line of reasoning is not found in either behavioral study, as they both only examined specific dog breeds. The journal is therefore the primary source for this. However, if you want to include this in your paper, you could write something like this: "Based on the fact that result X of the behavioral study with German Shepherds [Citation Primary Source 1] is almost identical to result X of the study with Chihuahuas [Citation Primary Source 2], the "scientific journal" concludes that this result could also be observed in other dog breeds [Citation Journal]."