The example 33 in the article "After the flop, you have initiative" of the Big Stack Strategy recommends to fold against a donk bet in the river (see for the hand details).

However, a similar hand is presented in question 11 of the quiz "Beginner Quiz (1) - NL Fullring". In this case it is recommended to call the donk bet in the river (see for the hand details).

I've calculated the equity for the first example.

Equity Win Tie
CO 69.71% 67.31% 2.40% AsKc
BU 30.29% 27.88% 2.40% QQ-22, AKs, K9s+, AhQh, AhJh, QhJh, AhTh, JhTh, Ah9h, Th9h, Ah8h, 9h8h, Ah7h, Ah6h, 7h6h, Ah5h, Ah4h, Ah3h, Ah2h, AKo, K9o+

We need to pay $10 to win $30.10, we need 33% equity, so I guess we can call.

On the other hand, the equity for the quiz is the following.

Equity Win Tie
MP1 23.88% 19.40% 4.48% QQ-22, AKs, KQs, AhQh, AhJh, AhTh, Ah9h, AKo
BU 76.12% 71.64% 4.48% AcKc

We need to pay $3.80 to win $20, which is 19% equity, so we can call too.

As I'm a beginner, I'm not sure if the hand ranges I've assigned are reasonable. Anyway, the only difference I see between the two hands is that a flush is possible in the first one and not in the second.

Any thoughts about this?