Normally I'd respond with an annoying "RTFA!" But you're right, the article really doesn't say where the tomato was.
I sent an artificial intelligence into the Internet for me to go searching for more information. Apparently the secret has simply not yet been revealed; this article says that the astronauts on board the station said they'd found it but that they didn't publicly explain further. Presumably NASA knows.
Both of those things are true. I used Bing Chat to go searching for me. It's an AI tool that goes through search results and tries to find the answer to a question among them.