Yup, that'd be his penis. I think I can see a scent gland too so I'm pretty confident you've got a boy there.
I see you're planning on getting him a buddy? Dwarfs don't need to have a cage mate; they're perfectly fine by themselves. Usually paired dwarfs have the biggest success rate if they're same gender, same litter (brothers, sisters). I have two brothers and they get on fairly well.
If you do introduce another hamster, I advise you to look up introduction methods and to be aware they may fall out via fighting. Then you'll need two cages, etc. etc. Sometimes the fights can result in a serious injury, or even death. It's worth weighing the pros and cons and finding out what you think is the best option.
If he's from a pet store he'll likely be a hybrid dwarf.