I guess you missed these bits from the article you linked to:
In February, a video aired from October 7 showed two men, including an individual identified as UNRWA social worker Faisal Ali Mussalem al-Naami outside Kibbutz Be’eri, taking the body of Jonathan Samerano, who was murdered by terrorists, and placing it in an SUV to take back to Gaza.
The picture of Palestinian terrorist Dalal Mughrabi who carried out the Coastal Road Massacre is featured on a classroom chalkboard in the Al-Zaytun Elementary School in Gaza run by the UNRWA Palestinian humanitarian aid agency. (Courtesy IMPACT-se)
In further damning revelations, IDF forces found in February a subterranean data center — complete with an electrical room, industrial battery power banks and living quarters for Hamas terrorists operating the computer servers — underneath UNRWA’s headquarters in Gaza City.
Numerous past reports have found that UNRWA schools and teachers continue to teach hatred of Jews and glorify terrorism, including a 2022 report by the IMPACT-SE organization that UNRWA textbooks continue to contain incitement. A 2023 report by the same organization along with the UN Watch group cited dozens of examples of social media posts by UNRWA employees that “glorify terrorism, encourage martyrdom, demonize Israelis and incite antisemitism.”
And the US State Department is free to make its own independent assessment of the credibility of the allegations, also informed by the findings of American intelligence agencies, which have their own independent sources in the Middle East. It doesn't have to be "proven" in the court of pubic opinion to be acted on by the US in an immigration matter.