They cannot prevent you from using the term the way the poster did on the forum.
There's a difference between what Doorbird says in their sales and marketing vs what a reporter for a newspaper or a poster on a forum says. In the case of Doorbird, they are using the ONVIF trademark promotionally, so it can be restricted.
In our over 10 years of covering ONVIF, ONVIF has been very reluctant to actually enforce its trademark so this is an interesting case. From 6 years ago, related ONVIF Affirms No Policing, Abuse Away!