On some level the headline is like "yeah, no shit," but the surprising thing is the claimed strength of the effect. 50% absenteeism increase for missing a birthday congratulations? Really?
I don't really mind but I take a slight objection to supposedly confidential data (like birthday) being widely shared even with good intentions.
Base rate is likely quite low.
I'm now somewhat interested in the study to see how they accounted for possible hidden factors.
If a team lead or manager spent the time to track birthdays and took time out of their day to have a 10 minute chat with someone on their birthday, they probably exhibit a number of other behaviors that could be summarized as "treating their employees as humans". That's the boss people tend to like to work with and possibly go another mile for them.
If tolerating your boss during a normal day takes 9 of your 12 spoons of energy for the day, it takes very little further push to be spiteful. At worst, they may force you to find another workplace with a better boss.