Well we could all wish that being or aiming to be helpful was a standard throughout the industry - sadly it in my experience, and even your notion of
unhelpful is indicative of the behaviour that has become more the par present times in regard of services offered - especially by larger companies which have adapted to the cheapest means to deal with external complaints.
As you point out, we are in the dark as to just what the hosting services were, there's mention of a server but we can only speculate. However the company does point out in their TOS, the customer is responsible for backing up their own data - but saying that we (as non customers) also don't know just how easy they allow the customer to do that.
Getting to the nature of the complaint - Obviously any company such as Hostinger has to position to minimise legal threats as per what they ultimately are responsible for hosting, and would do so by setting up processes to monitor for threats, detection measures such as looking for file fingerprints, possibly by using A.I. in a clever means. They'd also have a process to handle external complaints from people or companies on the web.
I can sort of guess what might have started the ball rolling,[1] (complaints by various domain providers) but that in itself, is not a proof, just that someone did not address those whatever they were issues in a timely manner. The person within Hostinger tasked to deal with the external complaint, given an apparent non reversal a suspended domain with the customer apparently simply ignoring the fact they have a suspended domain; isn't probably going to go to great depths to call in the system admin to confirm. Now they might be wrong given the small number of edge cases where it's all just a mix up or some other honest problem ... how many domains and with how many different providers?
[1] >They denied us access to our own data, even for non-suspended domains