I think he means (as I wondered too and had to look it up), what's the deal with "вон то" as opposed to "вон тот", which was the only form discussed in the grammar notes? Is it an agreement issue, a phonetic change, or something else?
Upon checking elsewhere, it appears to (logically enough, upon reflection) follow the same pattern as этот/эта/это, and is an agreement issue:
Вон тот = that (masculine thing)
Вон та = that (feminine thing)
Вон то = that (neuter thing)
You made me think! I think that "Вот" refers to something that is closer: "here" (and refers to a direction at which you might be pointing) . "Вон" is similar, but a direction in the sense of "there." "Там" refers to a place that is further away - "there." You can say "вон там" to mean "over there."
вон то is indicating an object over there. то is the neuter variant of тот- meaning "that" in the sense of that particular one. So вон то means "that one over there."
I am eager to be corrected by someone who knows more than me!