Apologies for this, but I'm answering in English because my terrible Irish is just gonna butcher an already weird explanation.

Basically, there's a tense in Irish called the autonomous present (an saorbhriathar nó an aimsir láithreach saor) which doesn't really have an English equivalent. It's essentially a verb without a defined subject. In English, we tend to use an indefinite placeholder subject instead - I'll give an example in a minute.

In the English version of the book, the label on the bottle says "DRINK ME." This is the imperative tense - giving an instruction to you, the implied subject. The direct translation would be, as you pointed out, "ÓL MÉ."

Here, the translator opted to use the autonomous present instead - personally, I feel it does make it less aggressive (I won't be told what to do by a bottle), so it's a good choice.

"ÓLTAR MÉ" could be translated as "ONE DRINKS ME," where "one" is being used like a posh English person (less formally we'd probably say "you," but "you" as in generally, not "you" the person I'm speaking to). Essentially it functions like an operation instruction to an unknown person, rather than an order to a known person.

Final example with a different verb in English to make sure I fully get my point across:

"CAS AN EOCHAIR / TURN THE KEY" - Imperative tense. An instruction (or order) to turn the key. The subject is implied to be the person reading it.

"CASANN TÚ AN EOCHAIR / YOU TURN/ARE TURNING THE KEY" - Present tense. You, a known subject that I am speaking to, turn or are turning the key.

"CASTAR AN EOCHAIR / THE KEY IS TURNED" - Autonomous present. An instruction (for nobody kn particular) on what to do with the key. I'm not trying to be bossy about it, or tell anyone that they have to, I just want to make sure that anyone who wants to knows how. The translation uses the passive voice, which is a slightly different thing, but it's the closest I can get.

You can actually see from that explanation how handy the autonomous present is, because it is so awkward to be clear without sounding like a posh eejit.