Hey buddy,
That just means he will be taking the old ball joint from your stock arm and placing it on the new arm because the SPC arm has a different ball joint, it's not a big problem...I actually just replaced my camber arm today with the hardrace arms from just jap which has exactly the same ball joint as the stock one.
Have a look at the link below it is the SPC arm:
http://www.streetunit.com/SPC_Adjustable_Camber_Arms_Pair_Inifiniti_G35_p/72125.htm
The link below is the Hardrace arms which I installed today, notice the ball joint is a cone shape similar to a stock one: That's why it was a straight fit.
https://www.justjap.com/store/product.php?productid=20161
All your mechanic will do is remove the stock ball joint and place it on the new arms.
Hope this makes more sense now.
Cheers,
Rush