Not sure the tracks you heard or the reviews you read but I wouldn't agree with that classification. When I think of smooth jazz Kenny G or Gearge Benson come to mind. She's not that.
According to Jazz Times "Sinne Eeg is likely the finest contemporary jazz singer you’ve yet to discover"
https://jazztimes.com/reviews/vox/sinne-eeg-dreams/ which really isn't true because I posted about her but...
Music Republic Magazine
http://www.musicrepublicmagazine.com/2017/12/sinne-eeg-dreams-stunt-1st-december...probably the best female jazz singer I have heard since the legends such as Sarah Vaughan and Ella Fitzgerald.
I don't think I know enough about jazz make that kind of statement but I can say her voice is special.
Maybe a really good "piano lounge" jazz would be a closer description. (I'm pissed because she actually was in Seattle Jazz Alley in February and I didn't know who she was so of course I didn't go).
I do have a thing for accordians so there might be a little bias on this album...
Marc Berthoumieux Accordion, Featured Artist
and horns
Randy Brecker Featured Artist, Flugelhorn
Jacob Christoffersen her piano player is pretty good too. Same review"Pianist Jacob Christoffersen has that Dave Grusin touch, and also put me in mind of the great and underrated Billy Taylor"
She also writes a lot of her own music which for me is also gets bonus points. She's not just a singer mouthing other peoples words. Nothing wrong with standards the first 100 times I heard them but I've heard em.
I don't really know how to classify jazz but she's along the same vein as Eva Cassidy or the Lisa Bassenge Trio - the A Sigh, A Song album. Patricia Barber would be in the same classification I would think but if I remember correctly Lon's not much of a Patricia Barber fan either.