If you copy or distribute the derivate work in either object code or executable form, you are obliged to make the source available.
Arguably anyone who has a phone, has had a copy in executable form distributed to them, and can ask for the source.
Arguably anyone who has a phone, has had a copy in executable form distributed to them, and can ask for the source.
Indeed, if you focus on the preceding bit about Google's in-house linux for their own servers, then there would be no distribution and arguably GPL2 could not force those modifications to be made public.
But I would imagine that he's probably quite versed in GPL2 and knows this -- so since he brought it up specifically, it suggests he was probably thinking at that point more about cases where distribution does happen (e.g. Android, embedded etc).
Perhaps he considers it a 'significant change' primarily if there's some sort of distribution ;)