It is different in that the OpenWrt patch structure encourages splitting up changes in a way that makes review for upstream merging easier.
Looking at random Google-forked git directories, all I see is uncommented auto-import commits without a readable commit message, without any indication as to what the changes are meant for or why they were added.
Stuff like that does not usually happen in OpenWrt-maintained patchsets.
I looked at jpeg, libxml2, bzip2 and a few others, and I found no useful information that could help with upstream merging at all.
Another issue is that in the android build system, you cannot build packages without making changes to them (you have to at least throw in some Android.mk files to replace the Makefiles), while in OpenWrt you can leave many packages as-is and use them with our package Makefiles and no patches at all