Alyssa's post mentions how lots of the work she's done has at least started as side projects while she's working on something else (Panfrost while at high school, M1 drivers while at Collabora). Obviously I'm not her so I can't say anything specific to her. In general, Apple doesn't allow its developers to work on open source projects on the side while employed at the company. I think this is a stupid idea that costs them a lot of talent, but I doubt Apple cares what I think. I've seen multiple cases where an active open source contributor gets hired by Apple, then their presence in open source communities vanishes. Based on all the open source work she's done so far, I think it would take a lot to make her stop all contributions like that.