Actually, there are three cases to consider:
1. You are looking at a report, and you have selected to view the results for
one group.
2. You are looking at a page like the quiz info page, where there is no clear
concept of the current group, but groups are in force, and you are in one or
more groups.
3. No groups in use of the course/quiz, or you are not associated with any
particular groups (e.g. admin on the quiz intro page).
In case 3. we want to keep the current wording [Attempts: 123]
In case 1. we need to reflect the currently selected group, so [Attempts 123
(45 from this group)]
In case 2. I think we need a wording like [Attempts 123 (67 from your groups)]
I also took the opportunity to improve the layout of this message slightly, and clarify the message that tells you that you cannot add or remove questions from the quiz if there are attemts.
Bug
Closed
Minor
In Moodle 1.9, this has changed to the simpler "Attempts: nnn", but it still does not take note of groups. However, the FIVE different places where this string used to be produced have now been merged into a single function, so it should be easier to fix in 1.9 now (but not really possible to back-port).