These words are likely spurious, probably added as a later interpolation by someone trying to explain why the woman was surprised that a Jew would be asking her for a drink. We know this because they are missing from older manuscripts.
Jews clearly had some dealings with Samaritans. History records that they fought each other! Yet, these spurious words make it sound like they had no contact at all, which is not true. The added text is probably just an attempt to explain that normally, in day-to-day life, the two communities kept separate.
It might be analogous to the Unionist and Nationalist populations in Northern Ireland in recent times. Generally, the two lead quite separate lives, going to different schools, churches, doctors surgeries, supporting different sports teams, and living in separate parts of Belfast. Yet this doesn’t mean that the two communities never, ever, have any contact with each other.