That means that the only elements to form positive ions with noble gas structures (apart from odd ones like scandium) are those in groups 1 and 2 of the Periodic Table and aluminium in group 3 (boron in group 3 doesn't form ions).
Negative ions are tidier! Those elements in Groups 5, 6 and 7 which form simple negative ions all have noble gas structures.
Does it mean that generally negative ions are luckier in achieving the noble gas form? Is there any trend behind this, or is it just a coincidence?
Why did he chose those particular three groups as an example? There are negative ions formed by elements in other groups too.