I hope (for your sake) that you don't have any users that can invoke their GDPR rights against you by virtue of their citizenship.
For the sake of incentivising companies to do the right thing, however, I hope you do have some EU or UK citizen users who do litigate or have their data protection authority investigate and formally punish Triplebyte, even if only to establish clear precedent here for the future.
Article 18 restriction of processing can apply here. Art. 25 "Data protection by design and by default" would seem to be relevant as well. The section I alluded to above is the latter half of 25(2), saying "In particular, such measures shall ensure that by default personal data are not made accessible without the individual’s intervention to an indefinite number of natural persons."
There's also the question of whether their consent or other grounds of processing suffice, which likely wouldn't for making anything public, but Article 25 makes it clear enough anyway this is illegal.
A European visiting the US and interacting with an American business does so under the protection of US law, not EU law. This is complicated in the case of Facebook and google because they also do business in Europe, so European courts can fine their European branch offices. But Triplebyte has no such EU presence that the European courts could pursue. And they don’t advertise European jobs. I suspect an EU citizen interacts with triplebyte legally the same way they would if they went to a cafe in SF while on vacation.
The opposite would be crazy. If triplebyte can be fined by the EU, that would also mean the government of Australia or China or Russia could arbitrarily levy fines against any US company if one of their citizens interacted with a US website one time. And everyone would put geo blocks on their websites to protect from liability.