The songs are by four different groups
The album cover is a compilation album cover made long after they had released their music and not by them and includes music of various styles. They don't all fit all of the genres mentioned on the cover
I genuinely don't think oja omoba (as one example) sounds much like delta blues but maybe because they're both using string instruments and singing there might be a few things that sound alike
There are different types of Blues in the USA. The Delta Blues is the version that people know the most about, but Louisiana and Texas had a different version. Listen to Freddie play a brand of Blues out of Texas:
Now listen to Gatemouth Brown play the same song using a Louisiana/Texas version of the Blues. It sounds more like Country music.
Now listen to Elmore James play a different song, but using playing Delta Blues with a slide guitar.
These are all different styles, but they are all playing different instruments as well as other instruments. There are so many other examples that it is ridiculous. They dude is playing a version of American Blues.