500' rule? Let's look at facts (don't take my word for it). I've added BOLD and COLOR to add emphasis:
https://www.faa.gov/about/office_or...re/media/FAA_Guide_to_Low-Flying_Aircraft.pdf
or
14 CFR § 91.119 - Minimum safe altitudes: General.
§ 91.119 Minimum safe altitudes: General.
Except when necessary for takeoff or landing, no
person may operate an
aircraft below the following altitudes:
(a)Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to
persons or property on the surface.
(b)Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the
aircraft.
(c)Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.
(d)Helicopters, powered parachutes, and weight-shift-control aircraft. If the operation is conducted without hazard to persons or property on the surface -
(1) A helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section, provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA; and
(2) A powered parachute or weight-shift-control aircraft may be operated at less than the minimums prescribed in paragraph (c) of this section.
So in certain instances and airplane, helicopter, para-glider etc can be below 500' and still be legal. It is OUR responsibility to do exactly as you did and SEE & AVOID.