The imam is saying that the person who asked the question should break his vow to obey the civil law if the civil law contradicts Sharia law. Sharia law is not comparable to the natural law, which is the basis of civil law for Christians and the basis of civil law in our country. Sharia law is more analogous to Levitical law, a perverse Levitical law. One of the aspects of Sharia law that is inimical to our form of government is the fact that Jews and Christians are to be "tolerated" as long as they pay a special, punitive tax and refrain from public religious displays. Members of other religions are treated more harshly. Under Sharia law, Mohammedan converts to Christianity are to be executed.
Now how can anyone who believes that Sharia law should supersede American law take an oath of allegiance to uphold the Constitution of the United States, which prohibits the establishment of a State religion and authorizes free exercise of religion?
The imam seems to be sayng that the questioner may take an oath to obey the U.S. Constitution and laws, reserving the caveat that the law of Allah is supreme. Now I certainly don't agree with the principles of Islam, but many Christians think that God's law is supreme and would feel justified in breaking a government law if it directly contradicted a biblical commandment. The fact that Muslims consider Jews and Christians to be unequal to themselves is a different issue.
No, that's Sharia law. When you think "Sharia law," think Saudi Arabia or the Taliban. Or you can do a search and see what fun the Mohammedans are having in Nigeria in attempting to impose Sharia law on the Christians there.
Mohammedanism and religious tolerance are simply inimical. There's a reason why there are no democratic Islamic countries. Islam is fundamentally linked to the State, and the world is divided between the "world of peace" (the Mohammedan world) and the "world of war" (the non-Mohammedan world).