I'm not so sure this is out of the ordinary. Some things to consider.
1. The non-Hispanic population grew by 7% over this period. So you're not comparing 45% to 0%.
2. Hispanics have the highest birth rate.
3. In addition to the birth rate, the group's growth benefits from immigration moreso than other groups.
4. To compare, Mexico's population is estimated to have grown 24% from 1990 to 2000. I'm not sure what their net immigration/emigration flow is. They lose a lot of people to the U.S., but also have a lot of immigrants from the rest of central America. I'm guessing that 24% is mostly based on birth rate and not a net positive flow of immigrants.