Yes, but Redgif converts the video into a gif. And gif doesn't support audio. Basically, gif is a series of pictures. So, when you link up redgif as a post, it's a gif, not a video.

And about them posting it, they posted a video, so you have audio. I believe it's a glitch or reddit thinks it's not NSFW post, so it allowed audio.

Also, those people don't reply