Even if it was the case, why would it result in that message?
But it is not the case (at least not in general):
My semi-professional guess is that the phone is booted off the network and told to reconnect in LTE when you hang up.
…and that takes a little bit of time, and the interaction between the modem and ofono can’t quite convey that this is normal behaviour. I see this too sometimes.
And what do i mean with “booted off” - i mean release with redirect. As this is not based on measurement reports, the mapping of coverage areas is approximate, and could end up having your phone look for an LTE cell that is not strong enough. Not sure what this looks like from GSM/2G (and too lazy to look at the spec) so basing this off UMTS/3G - there is bound to be something similar.
@mankir
What technology shows when you are in the call, and where do you end up afterwards?
(And do you have a lower preference than LTE in settings?)