Today I went to the masjid at the mall and when I started praying, a shiaa woman came to me and said that I was praying wrong. She was saying that I am not supposed to cross my hand on my belly and she also said that I am supposed to wear abbaya.
After that I overheard her talking to her daughter about how sunni people are kuffar
Do shiaa people pray differently? Do they think that Sunnis are kuffar?
There are some small differences between Shi'a and Sunni methods of prayer, although all of the core elements are the same.
One of differences, as you pointed out, is that Shi'a Muslims do not fold their hands in prayer. There is no requirement for Shi'a Muslim women to wear any particular garment during prayer, however; the rulings only outline to what extent the body must be covered.
For a more detailed list of some of the differences between Shi'a and Sunni prayer, see this answer. You may notice that none of the differences are large enough to change the essential form of the prayer; it is possible (and frequently the case) that Sunni and Shi'a Muslims pray side-by-side in the same congregation.
It is not at all a mainstream opinion of Shi'a Muslims that Sunni Muslims are kaafir. Unfortunately, sectarianism has led to strong polarizing emotions on all sides. The top Shi'a religious scholars and authorities do not hold this view.
