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In the 10-year old version of GIB's database, there is a rule which describes what it should do after the opponents make a penalty double.
When testing whether to bid 2♥, there are a few conditions it checks, but the most important is it checks whether [my hearts + min hearts partner showed] is strictly greater than [my clubs + min clubs partner showed]. So in this case, 4 + 5 > 2 + 4, so it bids 2♥. Seems reasonably logical.
Well, except it doesn't do that, because the programmers used the wrong code for counting the number of hearts it holds. Instead of (m=.), they've put m. instead. The latter works in some areas of the database, but not in the specific context used in that rule. So the number of hearts it holds is set to 0.
In the above case, it calculates 0 + 5, which is not bigger than 2 + 4, so it passes.
While it's always possible they updated this rule since then, it seems unlikely, because all other examples still match:
- give the robot 7 hearts and 1 club, and it still passes, because 0 + 5 is not greater than 1 + 4.
- give the robots 3 hearts and 0 clubs, and now it bids 2♥, because 0 + 5 is greater than 0 + 4.