It sounds like the video is saying (link with a time stamp corresponds the following)
we arrived at the cinema just in time to catch the start of the movie we arrived at the cinema just in time so we were going to the cinema we were hoping to catch the start of the movie we were running a bit late but we arrived at the cinema just in time to catch the start of the movie
What does "running" mean in "we were running a bit late"?
This post gives this explanation
i'm running a bit late: means you're explaining to the person that you're a little bit late to something; an event or an appointment. i will be a little bit late: means that you're telling them that you may not come to them on time.
I understand the "telling them" part, I cannot understand the "explaining" part, I didn't see any explanation, "you're" just informing/telling someone.
So, what does "running" mean in "running a bit late"?