I don't own a ScottEVest, but I have seen them. They do have concealed carry specific version (Enforcer?), but I haven't seen good reviews on it due to poor retention of the gun. (Concealment probably goes out the window when you put your vest on the back of a chair and the gun falls out.) A good comparison of how much weight a person is carrying with a fully loaded gun is this with some of the more popular 9mm models: Glock 19, Sig P229 and S&W M&P M2.0 - 30 oz., S&W Shield 24-25 oz. and CZ-75 Compact 32 oz. So any where from 1.5 to 2 pounds and there is the issue of 'printing' brought up by hooziewhutz. There are other more CC specific vests out there such as Rothco and HQ Issue and probably for less money.
That said most criminal elements see the issue as have a gun first and concealment and retention are afterthoughts, if given any thought at all. They don't go in for fanny packs, concealed carry vests or IWB holsters. A simple stick it in the waist band or if it will fit, in a pants pocket, does it for them.
I believe this guy had a gun, to at least control them, if not kill them. He likely had it in his pants pocket or waist band. There are tells when these criminals do this. A periodic hand to the waist to re-secure the gun if it is in the waist band, slight tugs to the shirt tail to ensure your shirt isn't riding up and a periodic glance down to make sure you're not printing. One of my thoughts is this guy could have made an awkward step to avoid a bad rail and had to reach to his waist to reposition the gun. Maybe his hand and foot placement just seemed off to Liberty when he approached them.