Though they've provided no reason to suspect JetBrains, nor have they said who is "investigating" the company, the article does say they may be compromised. If you rely on their software, it's probably a good idea to make sure you have a mitigation plan ready.
>the article does say they may be compromised
Same applies to any software. No software without a bug or an issue.
There is a somewhat higher chance of a critical security issue being announced for their software over the next month compared to January of last year. The accusation is unreliable, but it's a good idea to ensure you are prepared.
Sure, but let's be careful. These accusations could ruin their business, and the damage may be undoable - even if we later learn it was false.