They are not type approved by the manufacturer (MC stamped) The only car type tyre that has a MC stamp is the rear tyre used on the Can-Am Spyder.
OK but they don't HAVE to be!! There is definitely no Australian regulation, Federal, State, ADRs, anything.... that says a tyre on a motorcycle has to be stamped MC.
If it's on a motorcycle, it's a motorcyle tyre.
If it's on a wheelbarrow, it's a wheelbarrow tyre.
If it happened to me I'd take it to court, and win.
But then, of course, some shiny-arsed bureaucrat would take it upon himself to MAKE a regulation.... in the interests of safety, naturally. He'd know, wouldn't he.