I don't remember for sure, but I suspect the choice to have loop mean loop devices rather than control flow is due to programming being mostly off-topic on this site. Loop constructs in shells do come up from time to time, and it's natural to use the
loop tag in this sense.
Given the wide mismatch between documented meaning and actual use, I've retagged the loop device questions to loop-device and copied over the tag wiki.
It remains to be seen what to do with loop: should it be a synonym of control-flow? Or should it be blacklisted? Note that in addition to being a natural choice for the (rare) questions about loop constructs, it is likely to come up in migrations from Stack Overflow.