Well Xi never said that day. Curious where did you get that date or you just lying?
Easy tiger. Xi has publicly discussed his plans for a 'great rejuvenation' by 2049 - https://www.ft.com/content/d45119de-e11f-11e9-b112-9624ec9edc59.
This is widely understood to set a deadline for reunification with Taiwan: "His goal is a long-term one. He has pledged that by 2049, China will have achieved the “great rejuvenation of the Chinese nation”, a term that encapsulates both economic and territorial significance. Economically, it means that China will by then be a “fully-developed” country, surpassing the US to become the world’s leading economy. Territorially, it means reunifying with Taiwan, which split away from the mainland after the 1949 revolution." [emphasis mine]
Sure, he could bring the timeline for Taiwan reunification closer, but he's also criticised the US for 'goading China into attacking Taiwan', so it doesn't seem to be in his immediate plans - https://www.ft.com/content/7d6ca06c-d098-4a48-818e-112b97a9497a.