FFS. This thread is bordering on madness.
A 12 week old puppy is utterly incapable of going for anyone or anything. It has only been alive for 12 weeks; it hasn't the first clue how to behave yet. It certainly mustn't be crated all day.
Puppies play, and playing involves teeth and blood curdling noises and growls, especially if they're playing together. They are one of the finest examples of learning through play - their games teach them bite inhibition (google Ian Dunbar and bite inhibition), doggy manners and good behaviour.
Unfortunately, your pup picked the wrong person to try and play with. There may also have been an element of shock at being hurt; it is entirely possible your very young puppy hasn't felt pain before.
Don't leave the two of them together unsupervised, neither of them can possibly have a clue how to behave well together. Teach the puppy what it can and can't do in your home. A firm no when things are wrong, and a happy praise when things are right should be all it takes. Also bear in mind that collies are bred to snap; it is an instinct bred through them to enable them to do the job they are designed for. Not the end of the world, and certainly doesn't make them vicious but it needs remembering.
Don't make a big deal out of it, the dog is bright and will pick up on your worry but won't have any idea why you're concerned or what is going on. It is very likely to become nervous/unsure/confused about how to behave as a result.
Ignore all reference to pecking order and pack theory; it is very outdated and often plain wrong advice. I am distressed at the thought of someone turning a puppy onto its back to teach them anything at all. C Milan has a great deal to answer for. I am very glad he is not welcome in this country.