The Winchester white box is their generic targeting and training ammo. A FMJ bullet of traditional weight in handgun calibers. Winchester designates their own "white box" as the standard "target" ammo for 9mm. Note the wording on the box. Product Q4172. It only says target on the box.
They also market a "target" ammo, designed about 25 years ago to deal with lead pollution in indoor ranges. The use a proprietary name,"Winclean" to designate this difference. The difference is the head of the bullet is a flat point with exposed lead, and excellent profile for game or even defense. I own several 9mm handguns, including the smallest made, the KelTec PF9. The PF9 is not recommended for Plus P ammo because of it's 12.7 ounce weight, and frankly it does kick a bit. I carry Golden Sabre, Hyrda Shock and Corbon in my Glock 43 and 19 and other 9mms. I carry the Winclean in the PF9. It does a remarkable job in a short barrel where mushrooming often simply does not work.
White box looks like this if you buy it from Ammo.com. Notice the big letters target and practice?
Target AKA Winclean looks like this. Notice the same ballistics. Except this one does not say target and practice, it just says target. They also make the Winclean labeled as target in 124 and 147 grain.
Then the package some in 100 packs. But these just say "target" on the box if you go to the Winchester.com site. . And the same ballistics as the other two.
And they do 100 round packs of the regular white box too. So, they all appear to have the same ballistics. Some 50 rounds packs say target and some say target and practice. The bulk packs appear to tall say both. I cannot tell any difference, except I like the Winclean, if I can get them.
I think your assumption is correct, just a marketing deal... FWIW