It is a Steinway. You can see the name on the fallboard - and also, I went to Olafsson's recent Mozart recital at the Queen Elizabeth Hall in London, where he played this piece, and that was on a Steinway. I agree it might sound good on a Bluthner - I shall have to get the score, and then I can try it out! I think it would also sound good on my 1804 Broadwood - but I might have to alter those extreme bass notes!
It was, by the way, an astonishing recital - I thought it was a miracle of Mozart interpretation. On that basis, I would not hesitate to recommend getting the CD.
The concert was broadcast live on BBC Radio 3, and that is still available for another 9 days, here
. Highly recommended! Olfafsson's transcription of the Adagio from the Adagio of the G minor String Quintet is particularly moving.