I bet some clever person on the marketing team just went ahead and inserted the tag. My first experience on a large corporate dev team was eye-opening. While the core product code was version controlled and reviewed, the marketing team had the power to insert any kind of scripts onto the page without clearance. In theory, anything new on the page would require many ridiculous meetings. In practice, they could and did…
As a marketer and coder, I appreciate those loopholes to make sh*t work (I used to do it all of the time, and was pretty much the basis I was hired on at my previous job) :) although I would concede giving anyone the option if they don't have tech experience is a nightmare waiting to happen.
You bring up an interesting tangent that I'll speak to. As a marketer who needs to get things done, I feel you. At this organization, this was in the general interest of all of the middle managers as well. This encouraged more and more off the shelf "solutions" to be jammed in, and misorganization of the core team development. I was a contractor here, and the core code base was crammed with bandage quick fixes to the point where it was actually suggested to use Google tag manager to to change code on the fly for other third-party scripts.