How old is he? How long have you had him (from a puppy, or did you get him later)? How much training have you done with him, (trained on your own, took group classes, used a private trainer), and what training methods have you used?
Many dogs are not great with loose dogs charging up to them, so that by itself wouldn't necessarily be a huge concern. If you continue taking him into environments where he's going over threshold (reactivity, signs of fear/stress/anxiety, hypervigilance), it's unlikely to make him better and might well make him worse. If you're going to desensitize him to things that he's not comfortable with you need to work under threshold. That can be difficult to do on your own, because you either need controlled circumstances, or a place to work that has a good exit strategy so if things start to go bad you can bail.
No matter how good his obedience at home is, if you haven't worked around distractions, such as outdoors in the big wide world, it's going to fall apart.