Just from the title / tooltip of the actions, it's not clear what's the difference between the two:

This is what they do:
https://github.com/eamodio/vscode-gitlens/blob/5020fe18f0972f060a247976530b6e91fb97099d/src/git/gitService.ts#L1415-L1420
The harder part is how to explain the difference 😄 This StackOverflow answer is quite nice.
In GitLens' UI, it would at least be useful to add this:
- or, by changes (
-G)
- or, by changed lines (
-S)
Suggestion for respective tooltips:
- "Show commits whose diffs contain the pattern"
- "Show commits that add or delete the pattern"