First of all, it's good to realize that there is no reason any two variables should follow some specific relation.
More to the point of your question, judging from the plot alone, which is probably not a great idea (both fitting a real formula and checking statistics and coming up with a data story that explains any relationship are important steps), it is tempting to look for something based on the outliers that determine the overal shape when you look at this blob, I mean, the measurements with high sodium and high rating, however, I want to list some other explanations for this shape
- there are many more measurements with high rating, so also more outliers
- the relationship itself could be linear, the shape of the outliers coming from more measurements
- the error could be lognormal which could explain such a shape
- the error could be higher for higher values of rating
EDIT, after staring a bit more at the plot, it seems rating is cut off at 40. That's suspicious as well, you could imagine a (log)normal distribution in both directions without any correlation, then cutting it of there and you get this shape. Using that recipe, I created the scatterplot below. So the point is, there is no relation at all, but if you're looking at it you may be tempted to think there is something going on.