Hotel neighbors controlling Roku
If the TV in the hotel is a smartTV, it is likely that the guest (perhaps inadvertently) is actually casting to the TV, not your Roku device. This may help explain why Spotify seemed to be playing music "over" your Netflix. If the guest had actually launched Spotify on your Roku, then Netflix would have closed and Spotify would have launched and opened on your TV.
If your mobile app cannot see your Roku, then the hotel is likely using client isolation (which is good, and prevents devices on a network from discovering each other and interacting with each other...usually). It is unlikely also another Roku remote is being used as it would need to be paired with your device. (you can verify if any other remotes are connected/paired to your Roku by going to Settings/Remotes and Devices/Remotes and seeing if more than your remote is listed there.
Just for an added measure, go to Settings/System/Advanced System Settings/Control by Mobile Apps and change this setting to "Disabled". (this should prevent any 3rd party mobile apps from connecting to your Roku device. Unfortunately, this setting does not prevent the Roku mobile app from connecting if it can detect a Roku device, even in guest mode).
----
I would use the TV remote (not the Roku remote) and see if there are any wifi settings on the TV that can be disabled/turned off. (maybe call the front desk for some help if you can't find any). It is possible someone may just be familiar with a couple of network commands and a laptop and just going to be an annoyance until either the TV or the Roku is removed from the network. You will still be able to use your Roku if you can disable the wifi/ethernet capability of the TV. (if so equipped).
Do not factory reset the Roku device. You will likely have a difficult time setting it up again without a hotspot/alternative network. As a workaround, if you have a hotspot available to you, try connecting the Roku device to it via a password rather than the hotel wifi. (also limit the connection to 1 device in hotspot settings if available to you). If you still encounter the same issue with the actor, then you can be reasonably assured the problem is with the hotel TV wifi connection, and not the Roku device. (unlikely the actor is able to gain access to your hotspot and password w/o additional tools and knowledge).
Feel free to post the model number of the TV and can look into its capabilites and settings to see if that may be part of the problem.
edit... You can also go to Settings/Network/About. (note the IP address of the Roku device). Then perform a Network Connection Reset from Settings/System/Advanced System Settings/Network Connection Reset/Reset Connection. This may prompt the DHCP server of the hotel to issue new IP address to your connected Roku and also rid you of your pest.
