Perhaps it might be because...
...since it is a train, it is moving very very fast. Thus, if the old man looked outside the window, he would have seen a blur.
The only disadvantage is that he could have looked inside the train and noticed that it was not a blur, so perhaps an alternative could be....
...that since blind people hear better than average, he might have thought he was blind from how his eyes needed to adjust to the light$^\dagger$ and how the train was extremely loud $-$ during surgery, it had to be very quiet for the surgeons to concentrate, so the noise of the train might have appeared louder than usual.
Possible reason for the old man's impatience:
Hearing the noise of the train after being somewhere so quiet, he might have had the urge to take off his blindfold to see whether or not he was still blind (because of how the hearing of blind people can be affected). Or, as mentioned in the footer, perhaps he just had the blindfold for a long time and grew impatient.
However, I do not understand why the old man would kill himself. Perhaps the answer above is much more plausible $-$ if it was dark, the old man might have jumped off the train by pure accident (the OP never said in particular that he committed suicide). Also, if the train was in a tunnel, it would be darker outside and the train would sound much louder.
$^\dagger$as he might have been blindfolded for a long period of time.