Intent matters, come on, your arguments are ridiculuous. If one of the aesthetically pleasing files turns out to contain an exploit targeted at Cellebrite software, then it wouldn't be hard to convince a jury that this isn't a coincidence but intentional malware, especially combined with this wink-wink bragpost.
It's not Signal's job to secure third party software, they can intentionally post incompatible data, but it definitely is their job (just as everyone else's, mandated by criminal law) to abstain from any activities that would tamper with evidence. If that incompatible data isn't limited to randomness or crashes but contains, quoting the article "a file that executes arbitrary code on the Cellebrite machine" or "undetectably alter previous reports, compromise the integrity of future reports (perhaps at random!), or exfiltrate data from the Cellebrite machine" then it obviously was intentionally made that way, which crosses the line and at that point yes, it's definitely Signal's fault. If that gets actually executed on a machine owned not by Signal but e.g. some law enforcement agency, then Signal and any involved developers personally may face criminal charges.
It does not even need to involve any computer specific laws (though those are also likely to apply) - if there's an incident where evidence got disrupted, if there's evidence that this incident was caused by "aesthetically pleasing files" developed by Signal, and there's some evidence (e.g. this blogpost) that they made these files knowing that they might result in other evidence being destroyed - that's completely enough, that's tampering with evidence, a felony. Go directly to jail, do not collect $200, don't expect sympathy from law enforcement and the legal system.
In my personal opinion this is all FUD and scaremongering, because actually doing so carries little benefit and high risk for Signal. But, of course, no one can be sure.
It's not Signal's job to secure third party software, they can intentionally post incompatible data, but it definitely is their job (just as everyone else's, mandated by criminal law) to abstain from any activities that would tamper with evidence. If that incompatible data isn't limited to randomness or crashes but contains, quoting the article "a file that executes arbitrary code on the Cellebrite machine" or "undetectably alter previous reports, compromise the integrity of future reports (perhaps at random!), or exfiltrate data from the Cellebrite machine" then it obviously was intentionally made that way, which crosses the line and at that point yes, it's definitely Signal's fault. If that gets actually executed on a machine owned not by Signal but e.g. some law enforcement agency, then Signal and any involved developers personally may face criminal charges.
It does not even need to involve any computer specific laws (though those are also likely to apply) - if there's an incident where evidence got disrupted, if there's evidence that this incident was caused by "aesthetically pleasing files" developed by Signal, and there's some evidence (e.g. this blogpost) that they made these files knowing that they might result in other evidence being destroyed - that's completely enough, that's tampering with evidence, a felony. Go directly to jail, do not collect $200, don't expect sympathy from law enforcement and the legal system.
In my personal opinion this is all FUD and scaremongering, because actually doing so carries little benefit and high risk for Signal. But, of course, no one can be sure.