If the headline said "viruses" or "bacteria" instead of "plants", I'd definitely expect they meant live ones (and also that it's time to shelter-in-place even more than I already am). Given how ancient arctic pathogens are a relatively well-known popular culture meme, I also thought the headline means live plants.

Ha, then it's just me. Though... plant-based life coming out of the cold reminds me of

https://en.wikipedia.org/wiki/The_Thing_from_Another_World

Fossils aren't plants, they're rocks. Why would anyone assume you mean rocks when you say plants?

"Scientists discover rocks beneath mile-deep Greenland ice" maybe isn't quite as catchy, or as useful in conveying relevant information.

But it would have the advantage of being accurate. This is why they invented words like fossil.