I think that common sense should already tell people what you have stated here. There is basically no rule that doesn't have a exception in the animal kingdom, if you look at it on a global scale.
If some one was poking a snake with his finger and received a venomous bite, despite the snake having a rounded head shape, I'd say its because this person has acted foolishly, not because you gave bad advice.
The best advice in all cases is: "If you see a animal and dont know exactly what it is, leave it alone. And if you do know what it is, also leave it alone."
If someone needs to learn this the hard way, its not your fault.