My male friends are like my brothers and I would have no problem with my wife talking with them.
Men who are "jealous" if you want to call it that essentially know their friends well enough to know which ones can't be trusted.
It's possible the friend has shared some of his experiences with your husband which include sleeping with other married women or their friend brags about his sexual conquests. Naturally it's one thing for your husband to have a beer and watch a game with the guy without wanting him to spend time alone with his wife.
Too often the wife or significant other is offended because their mate appears to not trust (them) when in fact the man does not trust his own friend around them. Some men are great hanging out with other men but they see women as toys to play with either mentally or physically. If a man has a friend like that he wants to keep his friendship with these men separate from his relationship.
There is a difference between being "jealous" and being "protective" of your relationship/marriage. Jealous is tied to not wanting to "share" your mate's time or attention with others. However If one (knows) there is a "wolf" at the door and insists the door be kept shut that's not the same as being jealous.
There is a chance your husband may know something about his friend which you do not.