Thanks for the three videos and posting them in 4K! A little video 101 however. 30 fps came about for NTSC, the standard used in the US and some other countries. The frame rate is based on the AC line frequency of 60 hz (interlaced NTSC has two fields a 1/60 sec each). In Europe and the UK the AC line frequency is 50 hz and hence the PAL standard uses 25 fps. China uses PAL so they are catering to those customers with the 25 fps rate. The better rate to use would be 24 fps, a film standard, which can be adapted for both NTSC and PAL but not usually by the average customer even though our 4K TVs can deal with 24 fps. And we see 60 fps 4K becoming popular for sports. And I won't get into the drop frame conversion.
I have a NAXA 406 4K camera which probably has a Sony sensor but Sunplus cheesed on the software (MJPEG at 25 fps) using lower encoding settings to get it to work... cheap. Extracting individual frames (which can be done with FFMpeg) artifacts can be observed though no where near what you've shown in your videos. And also edge enhancement (yuck!) which doesn't appear to happen with the Thieye.