The immediate perception is that the runner (in blue) stopped short of the base (white square on ground) in order to trick the defender (in grey) into thinking that he was already safely on base (preventing the attempted tag by the defender from having any effect) and thus the defender did not actually bother to complete the tag, allowing the runner to then touch the base and establish a safe position. Alternatively, one might view it as the defender knowing that the runner has not yet touched the base, but then having a mental lapse of not completing the tag, due to the runner inexplicably stopping short. Either way, it appears that the runner got away with something that he should not have.
The reality is not readily apparent without additional context about the state of the game. At the beginning of the clip, you briefly see the catcher (man in heavy padding standing behind the batter) throwing the ball towards the defender seen later in the clip. Since the batter (in blue) is not making an attempt to run to first base and the catcher had the ball, we can conclude that the runner was apparently trying to steal a base (attempting to advance, without the ball being put into play by being hit by the batter). Note that during a steal attempt, the defender needs to specifically tag the runner (with a glove holding the ball) before he reaches the next base. However, the crucial part of missing context is that the pitch just thrown towards the batter (and caught by the catcher, right before the clip began) was ruled as a “ball” (an invalid pitch) and happened to be the fourth thrown at the batter, which lets the batter freely take first base and advances any other runner(s) that must be pushed forward. Actually, at very the beginning of the clip, you can also just barely see a bat flying away from the batter, which is presumably due to the batter throwing the bat back towards a helper that will collect and organize equipment. The batter did this since he was already aware at that point that a fourth ball had been ruled and that he was granted a free pass to first base. However, it is very easy to overlook this subtle detail, since it is only a blur seen for a fraction of a second at the beginning of the clip.
Since the batter was awarded a walk (a free pass to take first base, due to four balls being pitched), any attempted steal is nullified (essentially treated as having never happened) and the runner is anyways awarded a free pass to advance to second base (since he started at first base and was forced forwards by the batter taking first base). Thus, there was no need for the runner to attempt to reach second base before being tagged, nor did the defender need to attempt to tag him, since all of that no longer matters. Thus, given the full context, it becomes apparent that most likely the runner and defender also became aware of situation as it was unfolding (possibly due to the umpire in black informing them), and hence there was an apparently abrupt cessation of effort. At the very end, the runner extends his foot to touch the base and smiles, perhaps just to create a funny moment, rather than making an actual sneaky play.