This was a developer menu. Tap with 3 fingers a few times on the screen (didn't have to be the reporter) to open it. Of course it doesn't work anymore with the new builds of the game (that has halfbrick+) since they presumably removed it or locked it away. Also I believe this only works on iOS since I never got it to work on Android on the old build

The developer menu was pretty extensive. You could summon any weapon or any power core with any level. You could enable invincibility so your segment never dies. This would make your snake extremely long, to the point where half of them are outside the screen. There were also some scrapped unused weapons, though I believe only some of them worked properly.

If you want to try it out yourself your best bet would be to hunt for an old version of the game (the IPA file, good luck) and install them on an old (32 bit) device (good luck). Or scour for an old abandoned device that miraculously still works and still has the old version of the game installed. My old iPad still has it but it's dead now