The episode "Gwen 10" was actually a dream that Ben had Edit
1. The episode begins with Ben waking up, and it is a common trope for dreams to have the dreamer think that they are awake.
2. Even though he's gone back to the beginning of summer vacation, he still remembers getting the Omnitrix as well as all the adventures he had been on.
3. Vilgax appears in one piece, when he was actually severely injured at the beginning of the series and didn't fully recover until the first season finale. Dreams do not necessarily have to be completely accurate to reality.
With all these things noted, it's likely that the dream ended after Max got the Omnitrix and that Ben was relieved to see that he still had the Omnitrix after all.
The Episode "Goodbye and Good Ridance" is an alternate timeline by vilgax Edit
- Vilgax attacks in Ben's hometown.
- Ben's Parent's know about the Omnitrix.
- Everyone finds out about the Omnitrix and Ben being the alien hereos.
With all these noted, it is likley that vilgax went back in time, to atttack Ben's hometown, Ben's Parents find about the Omntrix while the first acutal time, was Grounded in Ben 10: Alien Force.