In fact nobody thinks it's particularly unlikely in these circumstances. Iran was on high alert for retaliation after their missile launch. Iranian authorities should have grounded all civilian aircraft - that's the conclusion I think all agreed on. Military and civilian systems don't always talk well with each other, so a transponder indicating "civilian jet" may not have been picked up by an old Soviet era anti-AC system which had a few seconds to decide what to do.

Very definite potential for fog of war - while everybody seems to agree the plane was shot down, nobody I saw thinks it was intentional.