Albert was actually not surprised at all that Riddle's diary had been stolen. Because this matter had been within his calculations all along. Ginny had simply waited until Harry's dormitory was empty to sneak in and take the diary, and Albert had merely given her a gentle push from behind, helping her make up her mind to do it.
Now was not yet the time for Albert to make contact with Riddle's diary. Given his abilities and caution, once he touched the diary, it would be impossible for him not to notice its suspicious nature.
Allowing the diary to return to Ginny Weasley's hands was beneficial for the "return" of the plot, or rather, he could not simply hand Riddle's diary directly over to Dumbledore; otherwise, how would he complete the upcoming system panel quests?
Chapter 564