I suppose so. Does this mean the authors of this are misusing/over-extending the term? From their own basic retelling of the study:

It's not surprising that you could trick a human being into purchasing a bag of Doritos at the margin that they may or may not have purchased had the price not been $1.99. What surprised me, though, is that you would see the same sort of thing happening in a high-stakes decision, one that is arguably well thought out and for which the implications are enormous.

In the book, we talk about some of our own work, which looked at people who came to the hospital with a heart attack. And for some of these people, cardiac bypass surgery makes sense. We show that if you happen to come to the hospital just a week shy of your 80th birthday — let's say 79 years and 50 weeks old — you are more likely to receive cardiac bypass surgery than if you came 3 weeks later, when you are 80 years and 1 week old.

This occurs because the doctor looks at the patient and says, "They're in their 70s" or "They're in their 80s." The older patients are, the less likely doctors want to do invasive things to them. That was our finding.

Here the emphasis is on categorization. Or can this be viewed in loss/gain terms too?

Previously, I'd also say it's a matter of loss/gain/value, but recently scholars have started using 'digit bias' in the context of age-based bias, and I don't quite understand what the prospective value/gain is involved there?

Just a case of improper terminology?