I believe that's with in the limits of the GPLv2.
TikTok have not provided a link to its source code, not are there instructions on their site or within the download package indicating where users can obtain the source code. Therefore, it's a violation.
Tiktok has not done that.
You also can't do it post-facto :)
In the CD era, it might have made sense to go with written offer if the source is far larger than the binary you ship (e.g you ship a 500MB game on CD, but the source would be 1400MB so that's like 3 CDs, ugh) and you're happy to periodically pay the office intern to burn some source CDs and post them off for the inquisitive customer who asked for them.
In the Internet era it definitely doesn't make sense. Just pop a link to the source next to the binaries and don't sweat it.
Unless, of course, you have no intention of complying anyway.
" 3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following: ...
b) Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or, "
Note accompany it.
The only exception is this: "If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code. "