Why are you assuming they are foreigners? Why do you assume these were not natives in their own country who held these feelings anyway? Do you observe and respect any festivities in the calendar at all? Christmas? Thanksgiving? Easter? Passover? Diwali? Why are these not "dumb superstitions", but other people's are?
You don't get to decide how somebody else is going to react to something, you only get to decide if you care.
You don't get to tell them to stop believing in Islam because they're in a country where that is a minority belief, you only get to decide if you care about offending them.
In this specific case, the lecturer clearly did care - she warned before the course and shortly before the lecture moved to showing that image. That's the issue here, not whether displaying the image was contentious or not: she showed due diligence and her faculty decided it was insufficient. So what would have been sufficient?
That we can have a debate about, but some BS about "western values" and a strawman argument about "submitting" to "superstitions" is not even worth me caring about, other than to call you out as making a statement completely typical of far right-wing xenophobes and racists. Please don't do that here.