Noticing something and reacting to it are very different things. Signal could fairly trivially grab all historical data for all online users within a fairly limited window. However it would be a one off event so the value proposition of such an act is dubious.
Show your working otherwise this is utterly spurious.
Anyway the difficulty of the task itself is traditionally taken to be irrelevant when performing cryptographic threat analysis. The question is about what is and is not mathematically impossible for an adversary to do.
Circling back up. Article author: Twitter might be untrustworthy and could bruteforce your keys. Use Signal.
Me: That's unreasonable. You also have to trust Signal.
Your answer just now: Why are people picking on Signal?!?
In fact, what the world really needs, rather than 3rd-party controlled encrypted messaging solutions like Twitter and Signal, is public apis for public key cryptography on non-trusted infrastructure, not tied to single groups. Everybody knows this. The reason that we instead have bodies like Signal -- a company that just so happens to tie every encrypted message to a real phone number and real human identity for no easily explained reason -- and the reason we have people who surely know better defending bodies like Signal in public, is an exercise left for the reader.
But I guess Signal doesn't implement it?
Edit: or Apple, whathaveyou
No free lunch. If comms security is that critical for you, outsourcing its assurance via trust is never going to cut it.