Sympathy crying?

Molly • 38 year old mom to my baby boy Oliver and pregnant with baby #2. Due 1/17/19

My boy Ollie will cry the instant he hears another baby cry.. even if he hears a squeal that he thinks will be a cry, he starts and I have to console him. He has a play group of 5 others toddlers ranging from 13-16 months and he is the only one who reacts like this. Anyone else experience this? I’m guessing is sympathy or he is scared? Emotional development