Isn't it offensive to freedom and human rights to ban students from offering prayer i.e. Namaz in college as the German government has done?

No, it isn't. In most Western countries there is a separation between the church and the state. A publicly funded university should not be used as a place to promote or practice religion. There are plenty of houses of worship in which religion may be freely practiced. In the US these "Houses of Worship" are exempt from paying the property taxes that individuals and business pay, which to many is more than enough of a government subsidy.