I would be kind of shocked if Equifax wasn't MITM'ing their internal web traffic. Doing so is somewhat par for the course if you want to be able to monitor and filter employee Internet activity, which most traditional corporations with significant security expectations do.
That being said, browser history and Google Account history are both reasonable places to look as well.
I am always a little amazed at the paper trail white collar criminals that get caught leave. If you think you might insider trade on some information, maybe you should talk to coworkers instead of texting them, and do your research on a personal PC[1] in private browsing on a coffee shop Wi-Fi network somewhere.
(None of this should constitute endorsing the crime, it's just like... from a privacy-minded standpoint... there's so much they could've done "better".)
[1]Honestly, if it's a six figure crime, why not a "burner PC". Buy a Chromebook with cash, and leave it at Goodwill when you're done. The last bit may even help soothe the guilty conscience a bit.