The instruction matrix they provide only includes 8086 instructions, not 186, 286 etc, which are all x86, hence the x at the start. From that wikipedia article, "The term "x86" came into being because the names of several successors to Intel's 8086 processor end in "86", including the 80186, 80286, 80386 and 80486. Colloquially, their names were "186", "286", "386" and "486"."
Comments
The instruction matrix they provide only includes 8086 instructions, not 186, 286 etc, which are all x86, hence the x at the start. From that wikipedia article, "The term "x86" came into being because the names of several successors to Intel's 8086 processor end in "86", including the 80186, 80286, 80386 and 80486. Colloquially, their names were "186", "286", "386" and "486"."
That wikipedia article lists the 8086 in its "Chronology of x86 processors" section as an x86-16 CPU.