Bootcamp is different on two identical Mac Pro 2013 towers, Windows 7 vs 8

OK, so we bought two identical Mac Pro 2013 towers, took them out of the box and updated the system, and checked to see if could use Bootcamp. Hopefully to install Windows 7, but, failing that, Windows 8. We got two different results:

One of the machines says only Windows 8 can be installed, but the other has a dialog about Windows 7.

The only difference here is that I messed around with the partitions on the second one. I may have jumped the gun and called one partition "BOOTCAMP" before being advised not to do so and attempting to get rid of that partition. My partition attempts have led to that system dialog...

What's the reason these two are different? IS it possible to install Windows 7?