Looks like he just misunderstood, I do that when I read fast too, or have not had my coffee.
A 4 inch concrete filled column will be just fine for what you are doing. It needs to be filled due to fire. If there where a fire the hollow post will fail, like spaghetti, and have bad consequences.
Have the lumber guys cut the column at the yard, and they sell the beam holders there also. You can weld them when they are in.
Also paint them when you are done...keeps em from rusting out.