During a tour in ...hmm..Belarusse, a very young Horowitz attended a Rubinstein recital, and was very impressed.
When Horowitz made his New York debut, his reputation had preceeded him. 'Everyone' was there, Rachmaninov, de Pachmann, Hoffmann, Rosenthal, the Lhevines. According to Rubinstein, at the last chord of the last piece, everyone was at their feet shouting, and Rubinstein shouted louder than anyone.
It also meant a slight personal trauma for him, making him start wondering about his own technical shortcomings.
Horowitz was given the advice to seek up Rubinstein in order to establish contacts, since Rubinstein knew 'everyone'. They socialised for a while, but R never felt quite at ease with him. It came to an end when H didn't turn up for a dinner, excusing himself with having forgot while he was at a horse race.
Speaking of him later, R usually said things like 'He has meant a lot for piano technique, but nothing for music.' I don't know that H ever mentioned Rubinstein after their falling out.