Yes, those could be temporary video files in the temp folder. I said could be because i am not sure where these programs put their temp video file. May be go to the forum of the software (I am pretty sure After Effects and Vegas have a forum of its own by Adobe and Sony), and ask people who use the software to confirm that the default folder for temporary video is indeed the temp folder.
I believe so. Other browsers typically hijack that folder as well, hence why it comes up under "Internet Explorer" when using CCleaner.