"He lets them past." vs "He lets them pass."

This was used when telling about how an elephant walked on the road, and the bus had to stop, and the driver had to give food to the elephant, after which the elephant got out of the way, so the bus was able to go.

He uses his four-tonne body to create a roadblock and demand a toll. When he receives a payment, he lets them past. Elephant Halts traffic for treats (see: 1:49-1:53)

The structure "He lets them past" suprised me, because we use verb in bare form after "let", so for example we say "Let me go., so I'd have expected "He lets them pass." in this case.

So what might be the reason in "He lets them PAST."?

There's a clear difference between "pass" and "past" in this context.

• To let someone past means they can move beyond a specific point.
• To let someone pass means they can proceed further unimpeded.

In some contexts, they may be used interchangeably, but consider some contexts where they are different. A security guard may say you can "go past" a gate meaning they are allowing you put yourself on the other side of it but may place further limitations on where you may go beyond that. However, a toll-booth operator may say you can "pass" meaning you can go through the barrier and travel on unimpeded.

Thinking about the elephant in your example, I don't perceive it was the elephant's intention to just let the traffic to the other side of him - he was granting them passage to continue. For that reason, I would have chosen 'pass', but really, the difference is so subtle that most native speakers wouldn't even think about this.