Default [Q] Digital Roaming?

On some AOSP ROMs, my Network says either Unknown or Digital Roaming.

1. Is it really roaming?

2. It only happens on ZVA radio. ZV8 is fine. Why?

Thanks!
Phone: Google Nexus 5 "hammerhead" ROM: LiquidSmooth F2FS Kernel: ElementalX 1.00
Tablet: Amazon Kindle Fire (Gen 1) "otterx" ROM: CM11-F2FS by Hashcode
Tablet: Google Nexus 10 "manta" ROM: LiquidSmooth F2FS-All Kernel: KT-Manta F2FS-All
Retired: Sprint Motorola Photon 4G "sunfire", Sprint LG G2 "LS980"