I felt the whole roof. I'm with the others, have him redo it. Felt has another function in that it is the backup layer in case the shingles leak for water being blown up underneath to snow melt and ice dams that allow water to soak through shingle seams.
In high wind you also want more nails. I thought friends go the extra mile for friends instead of taking shortcuts although in his defense, he probably does them all that way.