Thank you. I thought so since he was so careful about not being photographed.

Most likely just thatafter all, he would want as few people to see him as possible, since he's on the run from the law and there's always some chance someone might recognize him and report him to the authorities. It's obvious though, that he knows once he gets to Santa Rosa he'll be safely unrecognized there.
Also, the description of him would be that of a still pretty young, healthy man. By acting decrepit, he figures this will also lessen the chance of anyone who might have read some law enforcement bulletin linking that Charles Oakley with the ailing man on the train.