In this context, "cherry-picking" is a very negative term. This meaning comes from statistical analysis. The term is idiomatic and informal. It is not as negative as accusing someone of lying, but it strongly implies that they do not care whether they mislead.
Suppose you are writing an article about a sports team. The team won its first game, lost its next three games, and won its last two games. Looking at the team's complete record, you could say, "The team wins about half its games."
But suppose you want to argue that the team is really good (or getting better). You could choose to look at just the last two games, and say, "The team is on a two game winning streak."
Or suppose you want to argue that the team is bad. You could choose to say, "The team lost three in a row."
Both of these are examples of "cherry-picking": There are a bunch of "facts" ("cherries") to choose from out of all of the facts ("on the tree"). Instead of doing the hard work of considering all the facts ("picking all the cherries on the tree"), you pick facts that tend to support your argument, and ignore the rest.
There are also less severe examples of cherry picking. Suppose you said "The team has won the last two-thirds of the games it played." This is still cherry-picking, but not as bad as in the previous examples.