This is another myth about the ACT exam.
The ACT has a Science Section. But the questions are not based on your knowledge of Science. In the Science Section, there are reading passages which are excerpts from scientific journals, and students are required to solve questions based on the information given in the passage. So, essentially, it is a Reading Comprehension section where all the passages are Science passages.
So, even students from Humanities and Commerce background can do well on the ACT exam.