Here's my interpretation:
The three "Computer-n" hits on the Interior Explosion table (in HG2) do damage to "fib" computers, since this is physical damage from the mesons decaying into high-energy particles.
Any computer ("fib" or otherwise) is knocked out by the "Computer destroyed" critical hit, no matter how the critical hit came to be rolled.
These interpretations are based on the following bits:
The "Computer-n" hit description says that "fib" computers only ignore hits on the Radiation Damage Table. So this makes "computer-n" hits on the Interior Explosion table valid against "fib" computers.
That same reading can be interpreted to extend to the "Computer Destroyed" result on the Critical Hit table, since the Critical Hit table is =not= the Radiation Damage table and "fib" computers only ignore damage done on the Radiation Damage table.
Also the description of "Computer Destroyed" hit does not mention any exception for "fib" computers, so it can be presumed to apply to any computer, no matter how the critical hit came to be rolled.
Finally, HG2 does say that any roll resulting from another roll (such as a critical hit resulting from a roll on the radiation damage table) is unmodified, which can (if you're desperate) be read to mean that the cause of the damage done on the second roll (the one resulting from the first roll) is independent of the cause of the first roll: i.e., just because "radiation" caused the critical hit roll doesn't mean that we must somehow interpret the damage done by the critical hit as also being from "radiation."