they only started singing earlier this year这里为什么要用比较级earlier?

they only started singing earlier this year这里为什么要用比较级earlier?
又没有其他的事物比较,为什么用比较级啊?
我们听力的上下文给你们发上来，句子意思不是这样的。
Alex: Hey DaveI'm listening to a band called “The Toms”. Have you heard of them yet?
Dave: No, I haven't. Are they a new band?
Alex: Yes, they only started singing earlier this year. But they've already made two CDs.
Dave: Wow, they must be really popular.
根据意思来看，这是一个新乐队，不存在和去年的比较。