The only part of that post that remotely qualifies as modern is the mixed-case comments, which were likely added later on a 3270l, probably using the likes of XEDIT, some time in the 80's. XEDIT was a creature of CP/CMS, a virtual operating system which allowed one to run privileged code such as your example without needing exclusive use of an expensive mainframe. Using CP/CMS, you could treat a mainframe as if it were a PC.
Looks like there was a tabbing problem down in those EQUs. Still assembles due to a white space break, but it's ugly.
The white space break comes in comments, though, so it's irrelevant.
XEDIT started in VM/CMS IN 1980 IIRC. My thesis research predated that and was actually all done in a 28K MVS region on an IBM 029 keypunch. [They got XEDIT in TSO under MVS in 1985.] I did mixed case comments in 370 assembler as far back as 1984 on an IBM 3279-4.
Yes, I did debug supervisor code in VM/CMS, but I was a systems programmer at that time, and ran supervisor privileged production code all the time under DOS/VSE and MVS as well.