I don't have any numbers, but it is not entirely unfeasible that they would be. Police tend to react strongly if someone acts confrontationally with them, and this is something that autistic people might do more often. They don't mean harm, but how would the police know they don't?

Police can be trained to recognize various disorders and understand how to deal with them non-violently, but in the end, it may be difficult to see quickly that you should act differently if a non-compliant and threatening-looking person is autistic, compared to other non-compliant and threatening-looking persons.