The hi-res terrain data associated with the RTC product are only a resampling of the original SRTM/NED data that were used to correct the ASF RTC products, and not the ALOS low res DTM (30m) which produced using PRISM not PALSAR.
But of course you have every right to be confused. Here is another source for same info: Kristenson, Heidi. (2020). Re: ACCURACY OF ALOS PALSAR DEM (12*12 M Resolution)?. Retrieved from: www.researchgate.net/post/ACCURACY_OF_ALOS_PALSAR_DEM_1212_M_Resolution/5e6063ce0f95f19ff3364bc2/citation/download.
