In English we frequently "that's all" to indicate something was not more than something another person fears that it is. I'm finding it very hard to even find the right keywords to search for a similar phrase in German.
Mary: "You were really upset yesterday. I thought you were breaking up with me."
Joe: "Oh, sorry! No I just had a big fight with my family, that's all."
Or less dramatic yet still the same concept:
Horst: "Wow, your German has really improved lately!"
Evan: "No, not really. I just memorized by heart a few complicated songs, that's all".
So in either example, the speaker is using "that's all" to point out that the impression the other person has of something they did or something that happened they were involved in, is not what the other person thinks it is/was.
Specifically, they are expressing the sentiment that the underlying truth or facts of the matter that has triggered the other person's "inflated" or "exaggerated" perception is something much more mundane than what that other person (the witness to the event) believes it to be.
The closing phrase "that's all" is a way of finalizing and cementing that sentiment. It could also be expressed in English as "it only seems that way but it's something much less interesting or shocking".
Is there a similar phrase in German that communicates the same sentiment or message?