Why did the invasion of cambodia in 1970 surprise many people?

The 1970 invasion of Cambodia came as a surprise for two reasons. First, Nixon did not declare war on Cambodia so he didn't ask permission from Congress. He simply made it a part of the larger Vietnam War campaign. Second, it came at a time when Nixon was talking about slowly scaling back U.S. involvement in Vietnam and many saw this as doing just the opposite by widening the scope of the war.