He's simply clicking and dragging to perform a lasso function with the default Select tool. Yes, others on other forums have seen this bug, also. Fill out the feedback form, it'll get fixed in what I hope is a very soon released bug update.
I have noticed this too. Weirdly, when lassoing a single clip in the timeline (multicam) the colour board says I have selected multiple clips and does not allow me to adjust colour. If I click the clip instead of lassoing, it is fine and sees it as a single clip being selected.
The latest version of Command Post, beta 28, provides a solution for the clip selection bug. The plugin has a clever solution. It monitors when you are selecting clips and, if it detects other clips becoming selected, it deselect them. I have only been using it a short while, but it is very fast - I haven’t noticed any slowdown during the selection process. Check it out at commandpost.io. The app is funded by donations, so if you find it useful, drop a donation on them to keep it going.