Harry watched Hagrid getting redder and redder in the face as he
called for more wine, finally kissing Professor McGonagall on the
cheek, who, to Harry’s amazement, giggled and blushed, her top hat
lopsided. (Harry Potter and the Sorcerer’s Stone)
What does the bold-faced part mean? If it is the reason for Hagrid’s getting redder, I guess its tense needs to be perfect one: as he had called for more wine.
That sentence is perfectly fine, and it is similar to the following ones.
President Obama launched a pre-emptive attack against it as he called for federal immigration reform.
Alabama Governor Bob Riley was joined by Beth and Jug Twitty today, as he called for a boycott of travel to Aruba.
The crowd roared as he called for cutting defense to pay for domestic programs.
As is used to show the contemporaneity of two actions: The crowd roared when he called for a cutting defense, and Hagrid got redder when he drank more wine. In such a case, I would not use two different tenses; if I use the Simple Past with a clause, I will use the Simple Past also with the clause starting with as.