is this plagiarism?

I have been accused of plagiarism from my prof, since I have an answer from a facebook page based on our course, and a lot of students got their answers from there. The facebook page has previous labs and assignments from graduate students or senior students who have already done the course, thus there was around 14 students with the same mistake including me. But I went through my university web site and it states for the TEACHING ASSISTANT (TA) that:

Academic Dishonesty in Laboratory Environments

Academic dishonesty is a serious problem in undergraduate labs. This is partly because the culture of lab courses sometimes fosters plagiarism. Lab exercises may remain unchanged for years, making it relatively easy to obtain lab reports from previous students. Since students generally work in pairs, the distinction between acceptable and unacceptable collaboration can become blurred. And sometimes lab work is simply not taken as seriously as other scholarly work. The main forms of academic dishonesty in laboratory classes are:

Plagiarism in laboratory assignments and reports

Among some students there is an academic culture that accepts a certain degree of academic dishonesty in labs. Students buy and sell lab reports from the previous year and some try to "" junior students by “handing down” lab material. When such conduct is common, it becomes acceptable, and many students may not realize the element of dishonesty involved. In addition, in most cases the entire class is writing up the same report, so there is bound to be an enormous exchange of information.

If the paragraph above says that at this point this academic dishonesty becomes acceptable. Does that sort my issue at any point?