You are right, this info is from the wiki. On top of the Supermechs website, you have 3 buttons: contact, forum and guide. Button "guide" is a direct link to the wiki. The information about selling parts is from the entry "credits". Although, the entry "workshop" does not mention the function to sell parts.

So maybe someone updated the wiki in the past and changed the workshop text but forgot to change the credits text.

I personally think that a feature to sell items does make sense. The ratio of price to power level varies for different items. A simple leg gives you 5 power for 100 credits. Lets say item b would give you 5 power for 5000 credits than it would be much more clever to sell item b and buy simple legs. That way you would get much more power to upgrade other items.