I just learned about checkinstall. That’s really cool!
Me too! Is this how deb packages are usually made?
No, generally there is a debian directory with things like rules, control file, copyright etc.
A .deb is basically a tarball with some manifest information. You can build 'non-standard' packages in this way (also see FPM[1] - which will do this and more rpm etc). However if you ever want to upstream a package, there are guidelines that debian produce around this.