I will humbly disagree. Average is different from median and mode. I will probably not comment further.
I agree with you that the statistical term “average” in the specific sense of “arithmetic mean” is indeed a different quantity from the median and the mode.
However, it is also true that the statistical term “average” has another commonly recognized but less specific sense, widely used even among mathematicians: namely, signifying any of several different kinds of descriptive statistics that measure the central tendency of a data set. Among those different kinds of descriptive statistics that are referred to as “averages” are the median and the mode as well as the arithmetic mean.
I don’t blame anybody for wishing that the English language, especially its technical vocabulary, were more strictly precise and unambiguous than it actually is. But our preference for more precision and less ambiguity does not entitle us to pretend that imprecise and ambiguous technical terms simply don’t exist. They do, and “average” is one of them.
English usage is such that “average” is used rather liberally to mean all of those things. Merriam-Webster, for instance, defines “average” as:
Context is everything. In casual conversation, “average” can mean any of those three things, depending on how it’s presented. As I said, usually it means “mean,” but the median and mode are also possibilities. If there are some outliers skewing the data, I’m more apt to use median or mode to describe “average” in casual conversation. That’s why we have words like “mean,” “median” and “mode,” to be more precise when talking about “average.”
When I talk about the “mean” and explicitness is necessary, I say “mean,” because “average” is imprecise, at least in the context of non-technical English.