Modern LTE features a fairly high level of traffic security, although downgrade attacks remain a major problem. The article addresses this point: "The target of LTESNIFFER is to capture the wireless packets between the base station and the user. It can only obtain encrypted packets in most cases because it can’t know the cryptographic keys of users. However, some packets are transferred in plaintext by design." One of the reasons you here about cell-site simulators ("stingrays") a lot less these days is that improving security standards in the cellular network has made them less useful, although they are still widely employed and particularly rely on forcing downgrades to 3G.

Elsewhere, the article notes that one of the difficult things about sniffing LTE is that even the parameters used for the radio connection are encrypted, so some of them have to be inferred and guessed. That encryption isn't really intended as a security feature, we're talking about the modulation mode, but comes out of the fact that LTE revisions have erred on the side of caution with encrypting as much of the management traffic as practical. Much of this is a result of lessons learned with previous cellular protocols and protocols like WiFi, where unencrypted/unauthenticated management traffic has often become an attack vector.