What is this grouping?

I cannot figure out what is the yellow grouping? Nor do I understand how groupings like this showed green and blue bars. I understand what they are not how they got there or how to eliminate the grouping. I never use keywords or favorites ever. There are several of these groupings in the browser with the same bars.

I wanted to import a specific file just beneath the folder name and mistakenly clicked on the folder name and it started to import files. I stopped that and did cmnd z but these clips remained.

I am reluctant to just delete them without knowing what they are. 
Any help would be appreciated. 

Rich

Your browser is set to thumbnail mode with the time expanded.  The highlighted area is one single clip expanded over time.  Use the menu slider and move it all the way to the left to see just the single clip.

Shift-Z is your friend...