Is "Truth" Determined By Culture?

Ok, here's the email that a friend received from her professor. Basically, my friend was questioning some things that were in the textbook such as...

that because there is dispute over the nature of the earth, there isn't a real truth about its nature. It [the textbook] reads: "This example...illustrates that truth is never just one thing". "These kinds of beliefs, or truths, may change throughout our lives..."

Here is the professor's response to my friend's email:

From the perspective being advocated in the book, "truth" is a matter of agreements. Not all cultures define phenomena in the same way, and language plays a significant role in how we construct our understandings of things. For instance, in our culture, we have 7 basic colors and variations on those (red, orange, yellow, etc.). But there are other cultures that have only 3 words for colors. Do they perceive reality differently? Who's to say?

With regard to time, you do, indeed, put in an objective amount of time (which could be called objective truth), and your perceptions of it will vary (subjective truth). But we, as a culture, choose to define time in a particular way. Our culture is very linear with time (past, present, future). But other cultures do not have that linear sense. Islanders, for instance, typically measure time in terms of recurring cycles and don't have any sense of "future" or "end" that Western culture does.

So, is your sense of time a belief? Yes, from this perspective. You agree to and use a particular time measurement system that has been agreed upon, and around which ways of living are constructed.

Now after reading this, how would you respond. You don't have to respond to the entire email (that may take a while), but perhaps pick out 1-3 things from this and tell how you'd respond. Also, do you see the confusion between reality itself and knowledge of reality in here?