Reiss is saying: "some people call X the set of motivations which get called intrinsic, but actually there's no set X which is really shared between everyone".

Reiss is saying: "some people call X the set of motivations which get called intrinsic, but actually there's no set X which is really shared between everyone". As an example, children can be motivated by curiosity or by grades and competition (an "extrinsic" motivator). I imagine he'd agree that individuals have primary and secondary motivations, where secondary ones are all about filling some combination of primary ones. He's just saying that the primary ones differ between people (and maybe between times of day), and thus trying to debunk the idea that some motivators traditionally thought of as extrinsic (e.g. monetary reward) can never be primary.