It is developmentally age appropriate for a two-year-old to use his imagination. Imaginative play begins for the toddler at around age two. This is the reason that moms and dads give their toddlers pots, pans, and large wooden spoons and the young child might begin stirring and say he's making soup (or mixing a cake)!
I am more concerned by the fact that the stories your little son is "making up" involve aggression toward him. Here are some of the things for you to consider. Is it possible that a babysitter or nanny took your son to the park and another little boy hit or pushed him in sandbox? Sometimes, it's hard to pinpoint exactly where your child met another child who may have hit or pushed him when he was with you out in the world. When your child tells you that Bryan or Ryan hits or pushes him does he seem scared or anxious? Are there any changes in your child's sleeping, eating patterns, or mood? Is anyone yelling at your child? Sometimes, a child will categorize anger as hitting.
Another consideration is your child's speech and language development. Does he ever get mixed up when trying to express his thoughts and needs? Could it be possible that he is trying to say something different but lands on the words hit or pushed? If, after exploring these considerations you still feel uneasy I suggest you reach out to your pediatrician to request a referral to an experienced child psychologist whose expertise is getting inside the mind of a two-year-old. Take a deep breath and try not to worry until you know for sure there's a reason to.