Doubt it. Dash and Twilight are very similar in age, thus they were fillies around the same time. This was proven in Cutie Mark Chronicles, which shows all the Mane Six are similar in age, and all got their cutie marks at the same time. Thus, we can directly compare Shining Armor to this colt. Shining Armor looked like an actual young teenage pony when Twilight was a filly. This colt looks older than Shining Armor. Thus, father is much more likely than brother.