I massaged my smc muscle not for very long a half a minute but read that if touched the cartiod artieries it can cause a stroke? is that true?

Not necessarily: If you press too hard for too long you can get symptoms and if you stop the blood supply that is what happens with a stroke. This depends on how you touch the carotid and if you push too hard. Caution is advised

Carotid arteries: Two adverse reactions can occur if you significantly compress a carotid artery. One is stimulating the vagus nerve which can slow the heart rate and cause low blood pressure and fainting. The other is interfering with blood flow to the brain, but this usually also requires a plaque buildup in the artery. It's not a good idea to mess with the carotid artery, but your very gentle massage did no harm

Common sense: Messing around with a carotid artery can only cause a stroke if it is severely atherosclerotic and you release some cholesterol from plaques by physically breaking them. Even the kids' trick of slowing the pulse by pushing on your carotid sinus (at the very top, by your jawline) only works if you really push hard. If you're reasonably healthy, don't worry at all.