The word "to" is a bit special - it is actually not one word, but these are 5 different words, that are written the same.

1. One of the most important pronouns. Pronouns are *very* important in Polish. And yes, in Polish, the singular pronoun "to" (just this one) may, and sometimes has to, replace in some structures the plural pronouns "ci", "te" (these) and "tamci", "tamte" (those).
2. A particle, that replaces verb "być" (to be) in complex predicate: "Warszawa to stolica Polski" (Warsaw is the capital of Poland) , "Ania to dobra uczennica" (Ania is a good student) , "Czas to pieniądz" (Time is money); This particle may also replace a contruction "to jest" (this is, it is): "To ja" (This is me), "Kto to?" (who is this?), "To prawda" (This is true), "To tu" (It is here), "To za daleko" (It is too far away).
3. A connective that joins two sentences, of which the second is the consequence of the first: "Zdejmij koszulę, to ci przyszyję guzik" (Take off the shirt, then I'll sew the button), "Przyjechał wcześnie, to dużo załatwił" (He came early, so he arranged a lot). It may also connect sentences in a dialogue: "Kupiłem chleb. - To dobrze." (I bought a bread. - Good.)
4. A particle serving for greater expression: "Któż to przyszedł?" (Who came!?)
5. A particle serving to separate in a sentence the known or obvious information from something new: "W zeszłym roku o tej porze, to lało" (Last year in this season, it was heavily raining).

So, you are probably right that "to" could need a special lesson... But before one is prepared, this may be interesting to read: "to"

This, these, that, is, it, do, and even for giving your sentence more emotion.

Yes, it's wrong because you changed the subject.

Imagine: These aren't his cookies! Those are rocks that just look like cookies!

Meanwhile, your sentences clearly states that those are cookies, just not his.

Woops! Deleted, thanks for noticing.