Yep, it's Windows Phone's Cortana poking fun at Apple's Siri in a commercial. Again. Highlighting how Cortana and Windows Phone 8.1 are able to do things like offer reminders when a contact calls or prompt you with traffic reports, the ad definitely emphasizes the strong points of Cortana (notably, they're not poking at Google Now, which offers many of the same features). Meanwhile, the iPhone's gotten bigger with the iPhone 6 and iPhone 6 Plus.
Of course, while Cortana was the marquee feature of Windows Phone 8.1, Siri didn't get much of an update with iOS 8, with Apple instead focusing on other parts of the OS. Cortana's certainly impressive and leverages the best of Microsoft's many services in a way that Apple cannot without outside partnerships (including using Microsoft's Bing for Siri search results). And it's clearly a strong selling point for Windows Phone devices, but is a direct comparison with Siri really even a fair fight anymore? But after the long-running Mac vs. PC ads, perhaps it's fair game regardless.