Hi @zhenniwu
This is not “growth”. Your site was more-than-likely visited by a rouge-bot who does not follow any robots.txt rule and is already flagged by Google as a “rouge bot” and so their traffic is filtered from their stats.
There is little-to-nothing you can do about this unless you are willing to invest a lot of time and energy into bot-detection and blocking, which is mostly a waste of time (for most people).
This is just “life on the net as we know it” and nothing to even pay any attention too, for the most part.