Your friend is both right and wrong.
Your friend is right that option A (“were”) is the correct usage. When using conditional clauses (such as beginning with “if”) and when the condition is unreal or imaginary, the correct verb form is “were.”
For example, “If I were a painter, I would paint my own house.” The conditional unreal clause is “If I were a painter.” It establishes a condition for painting my own house, and it is unreal because I am not a painter.
Your friend is wrong that educated people never use option B (“was”). They do, although the incorrect usage is more common in speech than in writing.
When people speak casually, they tend to use speech habits and not analyze their word usage carefully. Indeed, the value of habits is that we can act without conscious decision-making, but it can lead to problems, as well. I probably use “was” in speech sometimes, although I am far more likely to use “were.” In my case, the correct usage is a trained, consciously developed habit. Now, “were” sounds more natural to me than “was.”
The reason many people use the wrong form, particularly in speech, is that people tend to use language the way they commonly hear the language, particularly how they heard the language used in their early years. The result is that the “wrong” usage sounds correct and natural and they don’t realize that they make mistakes.
We see the same problems with usage of “data” and “staff,” for example.