No, there’s no way to limit it to a single group. Not that I know of.
The parameter from group_list will be an array if there is more than 1 item selected and a string if only 1 item is selected.
So when there is just one item, you can do this:
-- [params]
-- group_list :groups
SELECT g.id,g.name
FROM groups g
WHERE g.name = :groups
ORDER BY g.name ASC
But since it’s an array, this below will work for both a single item and multiples:
-- [params]
-- group_list :groups
SELECT g.id,g.name
FROM groups g
WHERE g.name IN (:groups)
ORDER BY g.name ASC
But there is no way to tell the UI “only accept 1 item as the selection”.