It's correct. "I don't scare easy." As you can see here, when it's used without an object, "scare" means "to become frightened." http://www.dictionary.com/browse/scare?s=t So it does mean "I don't get scared easily."

It's a mistake in the sense that it's not grammatically correct; it's using an adjective where an adverb belongs (it should be "I don't scare so easily", and your assumption should be "I don't get scared that easily"), but it's not a mistake in the sense that it was done deliberately in the sure and certain knowledge that people speak like this all the time and so it'll be understood. There's a vast gulf between what the books say, and how people actually speak. And there's plenty of space within that gulf for a bunch of interesting stuff with respect to talking about language. I think that any question or answer about language is incomplete unless it covers all three axes of correctness, comprehensibility, and natural-ness. By sheer word-count, the vast majority of language generated is technically incorrect, but at the same time it's understood and natural-sounding. :)