[Adder]

Yet by the 500-1000’s approx, he was depicted very differently, with beard and longer hair.

See for example Byzantine churches and St. Mark’s mosaics in Venice.

[Varda]

I'll have to read the archeology report to see why they think it's a representation of Jesus.
The art I saw in Rome which as I recall was from the same period, did not attempt to depict Jesus. They were examples of the idea of the Good Shepherd.
The shepherds were everything from a man with longer hair and a beard to children. All Christians knew that Jesus was not an actual shepherd so it was not surprising that there was no standard model for the shepherd.
Until I read something that says that this was an attempt to depict Jesus, I'll be skeptical that that's what this image represents.