183. Pending the outcome of an inquiry, investigation or objection, or where a person has been charged with an offence, the Stewards may direct one or more of the following -
(a) that a horse shall not be nominated for or compete in a race;
(b) that a driver shall not drive or otherwise take part in a race;
(c) that the horses of certain connections shall not be nominated for or start in a race;
(d) that a licence or any other type of authority or permission be suspended.
They aren't guilty - they are being stood down pending the outcome of the investigation (in which innocence or guilt will then be decided).
Provison 183A also covers the horse racing with a positive swab.