To be honest, I wouldn't be surprised if Apple also compensated some high-value non-engineers in stock. To find the actual number of people who benefit, you would have to include them, plus you would have to add in all the people who don't work at Apple but own Apple stock directly or indirectly (for example, while I don't work at Apple, I probably own some stock because of my participation in a mutual fund).
I'm pretty certain that there are tens of thousands of people who see an increase in earnings because of Apple buybacks. The majority of them might be well-off since they are engineers or have the luxury of purchasing mutual funds, but I am hardly a millionaire or billionaire.
EDIT: Did more Googling; Apple's stock jumped around 12% after announcing their buyback, so the bonus is around 3%. I would love a $6000 bonus/year for the next few years. [0]
https://www.forbes.com/sites/chuckjones/2018/05/12/what-impa... [0]