Yes as said in table 3-1, only X1 chip must be contacted, others except memory are miscellaneous. And also as said in guide: Customer must determine if system thermal solution needs to contact all / select components on the PCB to make sure that they are maintained within the maximum temperature specifications listed in Table 3-1.
Whether the components in table 3-1 need to be contacted depends on use case, in general it is unnecessary, but as I said, it is a real tested result.
Regarding the θjc you said, we don’t have such data, while in simple you can take Tj as Tc since they are so close. Jetson nano has no θjp as it is sold without TTP. And as you can see in other Jetson platform thermal DG, such as Xavier, even the θjp is a calculated value by testing based on customer’s use case.