The main thing is that Google prefers to downlevel people who have external experience. I (male) had 5 years of experience, still was hired at L3. I know many others who have the same story.

So the L4 person probably had some better story/negotiation which allowed them to start at L4. It of course could be bias.

It was really frustrating for me to be at the same level as new grads, though on reflection, I was not at a the same level as other L4 employees around. Some transparency around these processes I think could help candidates a lot.

I think the bigger issue is that new-grad phds are almost always hired at L4. They are often less experienced at software engineering than someone with a bachelors and a few years of experience. So unless the person is being hired into an area that actually makes use of their phd, it seems that Google is just willing to pay for the title.