I run into those captcha's occasionally and generally reconnecting to a different VPN makes them go away. I always assume they are tied to bot activity coming through the same IP or range. I've scraped google in the past (years and years ago) and from what I recall you end up hitting the captchas after a set number of results in too short a period. Back then it was a pretty standard SEO activity, but it's usefulness was minimized when google started localizing results.