I would say that Detroit Steel Wheel clearly DOES know what they are talking about. An 1.5" difference in backspacking/offset is far from "basically the same".
IIRC the 22” OEM GM wheels offered for the K2XX gen SUVs/Trucks (possibly other generations) are offered in 2 offset sizes.
22” x 9” + 24
22” x 9” + 31 (maybe it's +30)
Here is a wheel diagram of 22” x 9” +24 w/ OEM 285/45/22 tires:
Backspacing of 151mm = 5.944”
View attachment 363567
Here is a wheel diagram of 22” x 9” +31 w/ OEM 285/45/22 tires:
Backspacing of 158mm = 6.220”
View attachment 363568
So what Detroit Steel is saying is that on their 22" steel wheels with their MAX back spacing they offer at 4.5" that wheel will stick out further than OEM wheels by roughly 1.5" (1-15/32"). Sticking out 1.5" would mean the wheels would poke out past the fender and stick out. Which would be an ok fitment if your truck was lifted or maybe even stock height, but you're not. Your truck is lowered by a fair amount. At your current static ride height you will want wheels that fit more towards the flush or even tucking inside the fender, not poking out past the fender.
Their 22” x 9” with backspacing at 4.5" is equivalent to a 22" x 9" with a -13 offset. Roughly. I say “roughly” because of conversions between metric and imperial dimensions.
Backspacing of 114mm = 4.488”
View attachment 363571