In the UK, PG stands for Parental Guidance, with a warning some scenes may be unsuitable for young children. That meant a lot of edgier films had that certificate for decades, but now we have a 12A rating that’s more or less equivalent to PG-13 in the US as well, rather than a jump from PG to 15 or 18 (the UK equivalent of R but those ages are mandatory minimum age, unlike 12A where children can attend if they are with an adult).

And yes, Temple of Doom did lead to the introduction of the PG-13 rating in the US. Here, all the cuts made to UK prints have since been restored, and the film now has a 12A certificate (the 12A certificate didn’t exist in 1984, and the BBFC didn’t want to give it a restrictive 15 certificate, so they made cuts for PG).

More on Temple of Doom (including my reaction as a nine year old) here, here if you’re interested. :)

https://fanfare.pub/indiana-jones-and-the-temple-of-doom-racist-sexist-too-violent-6d873271037