Can music be played simultaneously on Homepod and another device using the same account? When signed in with an Apple Music account on Homepod and another device, can I play music on both devices simultaneously? I believe it's not possible for e.g. iTunes and an iPhone; is Homepod an exception?

Specifically, it would be quite annoying if a family member at home started to play music and this disqualified me from listening on my iPhone on the go.
You can definitely listen to Apple Music on multiple devices simultaneously.

(In fact, my Homepod, Apple TV, and iPhone have an annoying propensity for all trying to play songs at the same time, instead of controlling one-another.)