Dear heart, simply ask him to show you how. Then sit back and wait. And wait. And wait.

You really need at least 30% butterfat in cream to be able to whip it. Light cream, by definition, can range from 18% to 30%, but almost any light cream you find on the market has only 20% fat. Even a 30% cream will not produce a very stable whipped cream. You're much better off with heavy whipping cream, at 36% or more fat.

So for the record: you are right and he is wrong.

Now, whoever told you to add butter to whipping cream - stop listening to that person. If you inadvertently overwhip cream so that it begins to form butter crystals, there is essentially no turning back. Adding butter to whipping cream in the first place is simply whipped cream suicide.