It could just mean they're interested in other people doing things differently.
One reaction is to look the other way and continue your journey, another one is engage in conversation and exchange ideas. Saying "I don't understand why some people (...)" can be a first step to this. Or, indeed, it can mean "they do things differently, therefore they're wrong". YMMV.
When people preface their statements by stating explicitly it's a rant, I think it's safe to assume it's the latter.