Mike, just about every lower ball joint I changed would only go in one way including Mustang ball joints that press in from the bottom because there are no bolts.
Page 8-8 in your Shop Manual shows the lower joint as it mounts from the bottom. Look at Fig.8 and Fig.9.
I'm going to stick my neck out and say, top joints normally mount from the top down and lower joints normally mount from the bottom up. There are exceptions where some early lower joints are sandwiched in the middle of the arm but again, there is only one way they fit.
Lower ball joints (and shock absorbers) mount through and bolted from the bottom so that the bolts do not bear suspension pressure. They are there to hold the ball joint assembly square to the lower arm.
Tell your mechanic that the tire pulls UP on the joint stud as the spring pulls down on the joint housing. It only makes sense to enter the lower joint from the bottom. I see pictures of other Ford cars that typically show the lower joint mounted from the bottom. - Dave