There must have been some output about downloading (or the fail of it) and the attempt to install it.
If you put igb to the list, instead of kmod-igb...
If it wasn't added, it won't be there ?
Something that doesn't exist, can't fail ...
I tried it both ways. The command line method didn't work at all. The custom build method didn't work but I'm not sure I did it right.
It's really no rocket science.. Downloaded image failes to extract - #32 by frollic.
I'll bet you can just build the image with the defaults and there would be no error messages. Like I said, I doubt I entered igb in the blank box correctly. If I didn't, I imagine it would be ignored.
The box isn't blank, it already contains the default packages...
I've built rockets and its easier. This should be plug and chug.
So you're a rocket scientist 
Apparently rockets are easier to build than clicking an arrow, pasting the kmod name and clicking build 
The big ones made of titanium, or small ones made of balsa wood?
I'm tempted to suggest to look for someone near your location who's more familiar with Linux and OpenWrt, so he can help you...
Success! Youtube to the rescue. Saw a grain image of someone creating a custom build and saw where I went wrong. Its is simple. First hurdle was I needed to extract with gzip and not the others I usually use. Next I needed to know what drivers I needed. And finally, the new driver is placed at the end of the default list in the custom build. Very good. Thanks ladies? and gentlemen for the help.
Great, it's finally working...it took a long way to come this far.
Would you please consider to mark the answer which was most helpful or the solution as such and your problem as solved?
Thank you.
And please consider to open an issue for this mate archive extractor tool.