This is most certainly a spelling mistake, check this out:

Dictionary: altbewährt

Edit: I think it means that the piece is beyond traditional jewelry and has a modern touch...

This is definitely a spelling mistake.
"bewehrt" is derived from "sich wehren", meaning protecting oneself (often in a military context); while "bewährt" means tested and proven; "alt" meand old.
"altbewährt" is a fixed phrase in German. If something is "alt bewährt", it has a lot of reputation, experience, history etc.

Really strange description, including spelling mistake. It means "breaks away from traditional elegance."