https://en.wikipedia.org/wiki/Unguided_bomb1. Thermal Detonators are magnetic, see TFA
Ok, fair enough.
However I can still go on about different aspects of that scene. Why did they need bomber ships to fly over it? You're telling me with all that technology, they can't attach mini thrusters to these bomblets to propel them towards a ship that they normally would not be able to get close to? Seriously - even here on Earth we have missiles, knowing full well that many high value targets cannot be approached like that. But it's even easier to implement this in space, given the lack of an atmosphere. They have used them before in SW, just not in certain instances where it makes the most sense.
The idea of bomber ships in the Star Wars galaxy is a humanized concept. I'm sure there would be instances where it is appropriate, but absolutely
not that scene. Resistance ships should have had a veritable smorgasbord of small, guided missiles that could be launched from nearby.
I'm definitely not the only one to write about Star Wars' excessive use of 'humanized' tech, either.
1. Thermal Detonators are magnetic, see TFA
I'm not entirely sure what this was referencing.