My wife and I have just bought a house from 1860 that was converted to steam radiators sometime in the early 1900s. I am doing a lot of research on how to service this system and have learned a lot.
Here is my answer to your question. Your husband is right. Steam radiators work via hot steam flowing through them. Cold steam turns to water and flows back to the furnace for the next boil. When you partially open the radiator valve, you limit flow into [and flow out of] the radiator. If they fill with water, they don't like it...they will knock and sometimes even stop working due to vapor lock. Moral of the story is that this type of system is to be SIZED correctly; that is to say, if it is too hot, the radiator is physically too big and should be swapped out for a less MASSive radiator. Less mass will absorb less heat.
There you have it. What is amazing to me is the nonchalance that plumbers have with regard to sizing a radiator. 'That looks good' is about the best guage I have heard.