why would that “crowd” present themselves as bots by modifying their user agent string? the point is to poison someone’s agent with sponsored “knowledge” over time.

That crowd doesn't -- but they often do the following:

- reject all 3rd party cookies

- selectively refuse to load 3rd party domains

- block javascript

- block webgl

- block webrtc

- block canvas

- use a generic user agent because "resist fingerprinting" is checked

- etc.

To a lot of sites, this makes you look like a bot. Most people don't go around deliberately spoofing their user agent these days. (and of course bots themselves can present whatever user agent they want.)