Because that is a possible Czech word order. It stresses "já".
Thats strange, normally the first word is the stressed one
Nope, the last one, it also usually brings the new information in the sentence.
The way a Czech speaker explained it to me is that the first word is the stressed word, which in this case is No. The speaker is making a correction. The last word is the secondary stress, in this case já (I), similar to how it would be emphasized in English. So I think you are both right. Another way to think about it is as two clauses, each with their own emphasis.
Well, yes. It also depends on the sentence. In the basoc SVO order you can emmphasize any word.
JÁ jsem Matěj.
Já JSEM Matěj.
Já jsem MAŤEJ.
Other word orders will only be possible when you strongly stress the last unit.
Matěj jsem JÁ.
I intentionally avoided the word stress for it is a complicated linguistic concept and it may not be the thing I have in mind. I just used the word "to stress something" in the everyday meaning, not the linguistic "sentence stress".
Is there any difference in tone or subtle meaning between "I am Matej" and "Matej is me"?
My best guess, and don't quote me on this, is that one is that you are introducing yourself to someone who didn't know your name, whereas in the other the person knows the name, but is looking for the person. But again, what do I know?