Isn't "sweet and sour" a name of dish? Does "sweet and sour" have two meanings in this song?
Ed Sheeran is likely making a reference to the "all-you-can-eat" restaurant mentioned earlier in the verse. He mentions that they "fill up a plate," and talk for hours about the "sweet and sour." Sweet and sour is a flavor commonly found in Chinese buffets, but can also be a metaphor for the sweet (good) and sour (difficult, bad) things in life. The clue to this is the lyric that follows after, "how your family is doing okay." You don't need to take this as an example of how "sweet and sour" is normally used. Song lyrics often use expressions in non-conventional ways, like this song.