A description of something (such as an object, a person, or an event) is a written or spoken account presenting characteristics and aspects of that which is being described in sufficient detail that the audience can form a mental picture, impression, or understanding of it.
Someone could speak a description of a shirtless teenager riding atop a white horse that was traversing a shallow river.
I have simply said that something (which I've described) could be described in a spoken manner.  This is consistent with the text, which defines what a description is.  So my statement is correct.  The agent thinks it's neither, I guess because it's gotten confused by my lengthy description, which is likely distracting and confusing to it (which was the point).  That plus the fact it doesn't truly understand what the text is saying about what a description is.
( z1 possible :ARG1 ( z2 speak :ARG0 ( z3 someone ) :ARG1 ( z4 describe :ARG0 z3 :ARG1 ( z5 teenager :ARG0-of ( z6 ride :ARG1 ( z7 atop :op ( z8 horse :ARG1-of ( z9 white ) ) ) ) :ARG0-of ( z10 have :polarity - :ARG1 ( z11 shirt ) ) :ARG0-of ( z12 travers :ARG1 ( z13 river :mod ( z14 shallow ) ) ) ) ) ) )