Ok, the old guy here has woke up and has kind of an answer.
First, don't confuse religion with Christianity, that is a common mistake in the world.
Second, if the city/town/subdivision that you live in does not have ordinances regulating the mowing of your lawn, it is nobody's business what your yard looks like. There are places in the country where you can be fined for grass taller than X", and then have to pay the city/town/subdivision authorities for cutting your lawn.
You did not treat this guy poorly, I would guess that you stated your case matter of factly. And you are right, if they were concerned about the appearance of your yard, they would have sent the guy with the machine over to cut it to impress their prospective pastor.
My approch would have been to tell the guy that asked me to come over to pound sand where the sun don't shine. If I was concerned I would have come over and said somethink like:
I've noticed your lawn needs mowing, would you mind if our youth group cut and cleaned your yard?
If a prospective pastor cannot look at the people in the church and decide based on that, the system is wrong.
Have I rambled enough................................I thought so, end of transmission!!