Well, this is a question for the lawyers and the judge, not for us here on JavaRanch!
You obviously want to speak up for your friend at work, but you need to be careful that your company doesn't decide you are collaborating with your friend to feed him inside information, as that could make life difficult for you. It's even possible that your company - or your friend - could ask you to make some kind of formal statement about the issue if you've been closely involved with the development of this product. So you'll need to tread a careful line between your loyalty to your friend and your loyalty to your employer (or at least to the fact that you don't want to lose your job!). And be careful not to suggest online that he copied your product idea.
It seems to be fashionable for tech companies to sue each other these days, although it's been going on
for decades. And it often seems to be just a way for Company A to threaten Company B with having to spend so much time/money for years of legal action that B will agree to pay some money to A just to avoid the much bigger costs of litigation. But it depends on the legal system e.g. the US courts seem to be much friendlier to big software companies than courts in Europe.
But it's also quite normal for one company to take an idea implemented by another company and re-implement it better or differently. Otherwise there'd only be one word-processor (and it wouldn't be
Word)! Depending on the legal system, the tests for theft of intellectual property can be quite strict, so your company might not win even if they do take legal action. Again, it would be a question for the courts to decide if your friend's company had really "stolen" anything from your company.
It's also quite normal to have non-competition clauses in your contract, although they usually only apply for a limited period. Many people question whether these clauses can be enforced legally, e.g. some legal systems include the idea of "reasonableness" in deciding whether something is legally enforceable, and it might not be reasonable to prohibit somebody from working in a similar field for the rest of their life just because they worked for your company for a few months. But you don't want to be the person to find this out to your own cost. Another one for the lawyers.
I'd say, let your company and your friend consult their lawyers on this, and be careful to stay out of it yourself if you can.