How is that the baptism of Christ when the Bible says that Jesus “came up out of the water”?
The fresco shows Him in the water, does it not?
Icons often show events, separated by time, together. In this case we see the Dove already above Him even though He is still in the water.
This is, by the way, a canonical “Baptism of Christ” icon, not an artistic rendition as sometimes is seen in later art.