Nothing interesting is going on behind the scenes.
1. The Liberals hold a minority government, and whipping the entire party rank and file into voting against the motion would not prevent it from passing.
2. The cabinet doesn't want to piss China off, and doesn't want to give their opponents ammunition (by voting against the motion), so it didn't show up to the vote.
3. This provides the cabinet with freedom of action, to quietly apologize to China in private, while not looking bad domestically. Or, alternatively, if world sentiment supports this position, and other parliaments and governments follow suit, this gives them the option to come out in support of this condemnation.
4. This will make a few rounds in the news cycle, maybe result in a small adjustment in foreign policy, but will not result in a major political shift in Canada.
tl;dr - the opposition is hammering the Liberal Cabinet on the morality of this issue, the rank-and-file Liberals go along with it, because they either have a conscience, or don't want to lose elections, while the Cabinet is playing Realpolitik.
For Americans, you can think of the Cabinet as the executive branch of government - closer in powers to the President, and their subordinate agencies. But unlike a President, the Cabinet, and the Prime Minister [1] can be removed by a 50/50 vote in Parliament.
[1] The Prime Minister in particular can also be removed by a 50/50 vote of their own party.