Simplified: you can make something illegal locally, but federal law will almost always win out.

Randomly inserting “allegedly” where it doesn't belong isn't a requirement for news organizations, its sloppiness. Inserting it appropriately may be a requirement or at least a reasonable effort to avoid overstepping the facts (and avoid liability for things like defamation where overstepping would harm reputations), but this is not that. The source they are attributing the claim to did not say that the data was allegedly used, they said that the data was IN FACT used. Either of these headlines would be reasonable and accurate given the facts in the body:

“Authorities say Flock cameras' data used for immigration enforcement”

or

“Flock cameras' data allegedly used for immigration enforcement”

The actual headline is, OTOH, just plain wrong.