Edit: I did a bit of research below, and 4% definitely does not seem accurate. I have no idea where the source for that 4% was :/
The number of votes cast in New York's 14th Congressional District election, 2018 was 141,122: https://ballotpedia.org/New_York%27s_14th_Congressional_Dist...
That's approximately 20% of the total population. I can find no info on what percentage of that 691,715 is eligible voters, but the 4% claim appears pretty ridiculous.
That's extremely common for local elections. For all the talk of money in politics, neither party could afford to fund opponents in every district.
> With 98 percent of precincts reporting as of Wednesday, the State Board of Elections shows 27,826 registered Democrats cast votes in Tuesday’s primary in New York’s 14th District. With 235,745 registered Democrats as of April, according to the BOE, this comes out to a turnout of around 11.8 percent.
NYT shows roughly 150,000 votes in the 14th precinct for the actual election: https://www.nytimes.com/elections/results/new-york-house-dis...
The population of the district is around 712,000 https://ballotpedia.org/New_York%27s_14th_Congressional_Dist...
So, the actual percentage is indeed higher than 4%. Even still, it's quite low.