Hello, and thanks for playing Gunbuds! Yes, Explory mode maps are procedurally generated (all levels in story mode as well, except the final level). Explory mode was something I added hastily at the end of production, so it didn't get as much attention as it needed which means that it has some bugs and is a bit confusing. It's not clear that there are secret walls that must be destroyed after picking up the corresponding "weapon upgrade" with the matching color / pattern. These secret walls are indistinguishable from other walls until they are shot - if you have the upgrade, they will be destroyed and if you don't, it will briefly change to show you what upgrade you need. These destructible blocks only show up at the border between different colored areas, so when you see that type of area, make like a Gunbud and start blastin'!
It's also simply possible that you ran into a bug with the level generator that I didn't catch, and if this is the case then I'm truly sorry. I'm always happy to take bug reports - you can either email gunbuds@gmail.com or DM @gunbuds on twitter if that's your sort of thing. Unfortunately, I'm not exactly sure where the shipped code for Gunbuds is - my main drive and backup drives both suffered a bad crash a few months ago so we might be stuck with any bugs you've found.
I'm glad you enjoyed the game, though - this was a huge part of my life for (way too many) years so I'm very happy to hear that people are having a good time with it.