I work for IPinfo.io (feel free to check your location data with us to see if we are correct as well). It is most likely that your ISP is sharing your zip code via a WHOIS/geofeed record.
For me, Firefox and without iCloud Private Relay engaged, Maxmind is within about 2km and doesn't get the city correct (but we're right on a border), and IPinfo is about 15km as the crow flies (and gets the city entirely wrong).