It could be also a form of anaprop, especially in the gulf region. Or mutual interference from surface based nav radars suffering from ducting.
What freq do your weather radars operate on? I'm assuming India band. If so then I cannot see how any fire control radars would have any significant effect on the display. Unless they were actively "jammed".
I cannot think of any situation where a civ airliner would be "jammed" for practice reasons. The only time a lock-on would occur is if an investigate procedure was called and the fire control radars would be used in conjunction with the surveillance radars and 10/10 10/11 / and a few other recievers.
Caveat,
This is purely from a navy point of view.