Just some food for thought...first, the Shat al Arab is claimed by both Iran and Iraq and the actual border down there is about as clear as the mud the place is composed of; second, I'm not saying this is necessarily the case with regard to the UAV's we've lost in Iran, but one of the nice things about UAV's is they are cheap and unmanned, making one way trips worth the loss of a UAV depending on the route; and third, we dropped cruise missiles all over several countries during our initial cruise missile attacks on Iraq. Many of them were older versions, and all have a known failure rate. Kind of a cost of doing business situation when you are launching several hundred cruise missiles.
" I see no harm in verifying the altitude shown on the picture"
I guess if you could get the dimensions of the ship in the picture and compare them to the dimensions of the GPS, you could do the math to figure out if 91m is correct. But really, if the Iranians were trying to jam or spoof anything, we'd know it. You can't jam or spoof passively.
Having said all that, you can always be counted on for looking at things from an alternative and logically feasible viewpoint. And...you could be right.