Sam –
There is a HUGE difference. In Christianity, at least in medieval times, there was such a thing as bowing to the cross, even if it was not done to “worship” it. There is no such thing as bowing to Muhammad. As for poskim being misinformed about other religions’ practices – if they lived among the religion they are discussing, fine. Otherwise it is pashut that it is more likely they were misinformed, and I have no idea why you think that is unlikely. This is compounded by the verifiable historical fact that Christians during the time of the Ran propagated patently false information about Moslems to make them appear as idol worshipers. And as I said earlier, the Ran lived in Christian Spain. You can find all this using Google and Wikipedia.