That would indicate IMO the same device is picking up different radio frequencies/bands across the 2 SIMs you're using - which would make sense since it's not always the case that a network piggybacking off the host network would have access to the full infrastructure. And if Smarty is a 'Light MVNO' then they simply get access to the capacity/bandwidth/antennas that they have negotiated since it is less of a burden for them to manage full network operations. Just a thought.
You definitely have 5G selected as the 'network type' on your device I'm assuming?
Bear in mind certain phones will auto switch to the network type that they `feel` offers fastest connectivity/ stronger signal, in other words they 'avoid using 5G unless its really required for what you are doing' to save battery etc. On Pixel phones I've seen this as 'Adaptive Connectivity' or 'Smart 5G' on other Androids. That might affect when and where you get 5G.
