I've just found out the novel is by H. G. Wells, so what I am going to say may not capture all the nuances that Wells imbued into the title. The noun phrase "by chance" primarily reminds me of randomness, haphazardness, and intransigence. Just as a game of chance is dictated by the random numbers one gets from the roll of dice, so the work looks to me a travelog of a bicycle rider whose chance (i.e., random) encounters with people will have bearings on his life.
This is what I gathered from a hurried look at the
Wikipedia article of the work.