No, not necessarily... I am a home owner and I could use a cubby room type of space for just organizing various gardening stuff or whatever. Some people like a little bit of structure to what otherwise is a useless air pocket.

Maybe the prior owner just walled it off for a dry storage space. Nothing more... nothing less.

Just use a tray and use that wet tape compound for plastering/taping drywall and use a good sized plastering tool so that you can cover a lot of sq ft at a time.

Honestly, I would avoid radiant heating. I have it in my 2k sq ft ranch style home here in the Bay Area (prior owner put it in) and I find it more finicky than the normal forced air type of heating. Maybe just me....