If those factors are established in Universe, fine. I assume things are like reality unless it's already established they aren't, so if they aren't, they aren't.
To be fair, they're like, space missiles.
Seriously, though, they just went with "Him being small caused him to be repelled instead." You see him basically be thrown back along the edge of the blast:
Obviously the real life physics can be debated about whether the blast would actually repel him like that or not, but the whole "Something of that size/mass could be repelled and survive it/the fall/whatever" is based on real science and not just something they completely pulled out of their ass. It probably doesn't truly apply to this kind of explosion, but they decided it does, and so there's internal logic behind "Going small saved his life."
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Seplito Nash, Smelling Like the Vault since 1996 Step FOUR! Get Paid!
