> The officers, we later learned, had been told that Samuel was an ”active threat.”

The ambassador does not have the right to lie about someone being an active threat.

> A few days before the event, Samuel had published on his Instagram that ambassador White tacitly threatened an American and Belgian resident after that citizen urged the Zac Brown Band not to perform at the event

No right to threaten either.

> how we had got into the event (that the American embassy invited us to).Eventually, they accepted that we were journalists and that they disagreed with detaining us.

You dont get to invite journalists and then try to get police to detain them either.