You see the planets and stars in the background right? The galaxy you see in the picture is nowhere in sight. You can see planets and stars the entire time when his flew to the alien planet in the second episode.
There can be 2 reasons behind this:
1) There are regular amount of galaxies in DB universe
2) There are immeasurable amount of orphan planets and stars outside the galaxies which makes the 4 galaxy universe statement pointless since DB universe has the same amount of matter as any other regular universe
If there was only 4 galaxies then rest of the universe would appear void the whole time Whis flew outside the galaxies. That's not the case as we see in Episode 2