Zenyatta doesn't know Rico beyond the fact that they are on this mission together, but he saw Eclipso encase the man in dark energy. Something must be done. Not knowing a person never stopped him from aiding them.

"You be--" His words are forgotten at the sensation of Rico growing taller. But, that's not it at all. Zenyatta looks down at the ground beneath him, puzzled. It was as if gravity chose that moment to become stronger and caused Zenyatta to hover lower. The moment passes quickly. Zenyatta returns his normal hovering height. "You belong only to yourself, but this... this is not you. It is Eclipso."