Which meaning of "but"? Or just wrongly noted example sentence?

Question

In the Cambridge Dictionary's article "the icing of the cake", the following example is given:

I was just content to see my daughter in such a stable relationship but a grandchild, that really was the icing on the cake.

Even after checking all meanings of "but" I cannot figure out which meaning of "but" is meant here. Rather it seems to me that the above example sentence is noted wrongly, and the right notation should be:

I was just content to see my daughter in such a stable relationship.
But a grandchild (=having a grandchild, moreover), that really was the icing on the cake.

Is my assumption right/wrong?

Answer 1

"I was just content" in this context implies that the writer might not dare for more than their daughter being in such a stable relationship, but the "but" says they got more in the form of a grandchild, which was the icing on the cake i.e. something that elevated an already positive situation.