Sometimes it means that he actually has to go to a whole other town to complete some business he is doing. Sometimes it means he wants to have an affair. If the guy is a warehouse worker... He will not really ever need to go out of town. If he is a lawyer or a business executive of some sort... He might have to go out of town. Know your guy..... and you will know if he tells you the truth.
Sure, sometimes guys might lie, but he may actually have to go out for business. Give the guy the benefit of the doubt. If you get the idea that he's deceiving you and he's being shady, or you wind up with evidence that he's seeing another woman, drop him like a hot potato.