It’s kind of an opening line before I stress that the sushi

In short, the particle が serves as an introduction here before addressing the real problem. In this lesson you will see that the ga particle can be used as an introduction in the first sentence with no “but” value. This is an introduction before you ask the question yourself. In Example 1 this means that the sushi you ate was very tasty. You will often use this pattern of Japanese particle sentences over the phone. In this sentence, sentence 2 is always what you want to emphasize. In the following example, it is used to combine a sentence with a positive meaning and a word with a negative meaning in the sentence.