Who are "they"? The liver toxicity of acetaminophen (paracetamol) is well known and thoroughly documented, but it takes a lot more than 500 mg for toxic reactions to occur. Several preparations contain 750 mg or even 1000 mg per dose, and a daily intake of 3000 mg is generally considere safe, even with long term use. The OP was talking about a one-time intake of 2 1/2 pills, 1250 mg acetaminophen, which is perfectly safe.
Even taking 4000 mg of acetaminophen during the day is considered safe. And you are quite right, if only we speak of a one-time intake. But when acetaminophen is taken regularly in high doses it may be really dangerous. It has to be taken into account.
Anyway, your warning comes a bit late, as this thread is nearly a year old.
I've come across it while surfing the web, so the thread is available and can be read by other surfers, too. Perhaps, they may find it interesting.