as someone who has relevant experience in animation i can at least tell you that if these are indeed fake, then they were either faked by someone with intimate knowledge of how animation looks from inside an animation studio or zach is bullshitting everyone and i can explain why:
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this part is the timecode, it shows you the hour, minutes, seconds and current frame the video is paused, this overlay is useful for keeping everything orderly and give you information on how things are ordered (animation teams work on scenes individually and production is often further split to international outsource teams). time seems to progress between the two pictures in a sensible way
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another part is the filename for the video as listed on the corner of the picture also matches popular naming conventions in animation.
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SF = title of the show "Smiling Friends"
SC 03= no. of the scene (it is a little unusual that the scene number is so low, you can't be three scenes into over an hour of animation, scenes are when the camera cuts away basically but it could still work if the scenes refer to story chapters maybe? i couldnt know
anim= i'm guessing theyre referring to the final animation (meaning that this version is as close to finished as it can be, assuming comp work is done), as opposed to posing, rough, storyboards, clean/ink and paint etc. just something else to keep files orderly
TK3= take three, this animation has gone over three revisions, whether it was sent back for fixes three times in cleanup/comp or if the scene number is increased through other means (for example, whenever we clean up rough animation thats come in we up the version number regardless of how many times we revisit it until its perfect).
this logic follows with the next image though its fairly obvious why the filename is shorter
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EC= end credits. simple.
the thing at the bottom is just a watermark. its usually placed there to tell which company is in charge of the production of the series. self explanatory. the only additional information i can glean is that MAYBE this means that the leaks were leaked directly from williams street studios but I could be wrong. from what i can see its probably an overlay done automatically in after effects, which is good for comp work but i could be wrong (since i don't work in comp work though i have seen my coworkers).