This is because Roon will read the tag information (including MQA tag) and display just below the album art. This is probably a MQA tagged but a 16/44.1 FLAC version.
Ultimately, when Roon try to playback and display in the signal path, it will look for authentication MQA signals encoded in the stream, if this is not present it will treat like a normal FLAC. Normally when Roon displays ‘Versions’, it will contains one MQA encoded and the other a 16/44.1 FLAC versions.
Roon should recognize the MQA stream regardless of whether the album is in your library or played “directly” from Tidal (i.e., not assigned to your library). Maybe a fluke? Have you tried removing it from the library and playing it straight from Tidal again to see if the behavior repeats?
I was testing it and found taht like you, if I did not have the album added to the library, when I clicked on the play icon for the work (not individual parts) then it would not MQA decode. However, if I just clicked on an individual part it would MQA decode. I wonder if you have the same experience.