Waiting for ClevelandKentEvans to show up but I have noticed that folks in the past LOVED nicknames as first names and there's a lot of it, so I'm assuming Arta is typically short for Art* names, whether male or female.
There's been several submissions of this name too, which show it's usage in different places, so there could be numerous reasons.
https://www.behindthename.com/name/arta/submitted
My PNLs = http://www.behindthename.com/pnl/37275
My ↑ Faves: Remy and Eseld
List ↑ Rated: Henry and Alice (main) / Caspian & Guinevere (GP) / James & Charlotte (top25)
List ↓ Rated: Calhoun and Venla (main) / Bedwyr & Oniria (GP) / Thane & Eydis (top25)