Agreed on the twitter part, but the FB part feels like a pure conspiracy at best, and is just factually provable to be false. For one, Vine was killed off in September 2017, which is the same month that TikTok became available internationally.
To add, the acquisition happened in november 2017[0], which is after Vine had already been killed off. Vine had 200mil users as of 2015, while it took musical.ly until May 2017 to get there. Which is also, months after Vine had already been dead, and over half a year after Vine had announced the upcoming shutdown (those numbers and dates are all from the wikipedia pages of the companies mentioned).
0. https://techcrunch.com/2017/11/09/chinas-toutiao-is-buying-m...
https://www.theverge.com/2016/10/28/13456208/why-vine-died-t...
TikTok is an international version of Douyin, which was released in the Chinese market in September 2016.[10] It launched in 2017 for iOS and Android in most markets outside of mainland China; however, it became available worldwide only after merging with another Chinese social media service, Musical.ly, on 2 August 2018.
From the links above Vine was already dying if not completely dead before TikTok was ascendent.
The irony is there was a product, Vine, that filled this niche but it was ultimately killed by Facebook (who promoted Tiktok because they didn't want Vine making inroads with their users) and Twitter (by not developing it further).