Insider trade on Splunk acquisition?

Is there any legit way in which whoever made this trade could have got a wind of a potential acquisition without relying on inside knowledge?

Knowing about the acquisition puts you in possession of material nonpublic information. It's unlawful to trade on the basis of such information whether you work at the company or not. Passing it along is 'tipping' and acting on it is still 'insider trading.'

My understanding is that having material nonpublic information is not—in itself—enough to make a trade illegal. As long as you're a true outsider, and didn't get that info using illegal means, you can trade on it.

Maybe this whale was tracking tail numbers, drove down to the executive airport, and saw that Cisco's chief M&A guy had a huge grin on his face as he stepped onto the plane.

(Okay, I doubt that highly, but it is a scenario)