Look what I got from the forge...
Happens all the time. Anything from the Forge is a gamble. It might be awesome, it might suck, and it might be soulbound. It may be related to what you put in (for example if one of the items you used was soulbound), but it seems to be random in my experience.
All you can do with that piece is either A. destroy it or B. hold onto it as more mystic gambling fodder.
It happens all the time unfortunately. You cannot salvage it nor can you sell it. (these two over sights by the developer aren’t great for the mystic forge.