It means that if someone now puts a bet on, they will win less money (should the bet win), than they would have won before the odds were cut. Bookmakers do this for one of two reason.
1. Lots of money was bet at the higher odds, so the Bookmakers balance their books by increasing the odds on the other market and lowering the odds on the one that is getting more money from punters.
2. Something made it statically more likely for the that pick to win. Forgetting about WWE for a second, and looking at football, bookmakers would cut the odds on one team if there was a rumor the other football team was going to field a side with a weak squad of players.
Ultimately, there is reason to believe bookmakers now think that Cena has a greater chance of winning tonight due the recent fluctuations in the betting market. Cena is not favourite though - Lesnar still is.
The fact that WWE is predetermined really makes it hard to figure out why odds fluctuate. For example, in the last few hours before the Royal Rumble, Batista was the favourite to win, but at one point Bryan's odds were drastically cut to make him the odds on favourite. A lot of people thought this meant word got out from WWE that he was going to win the Rumble, but this ended up been wrong.
tldr: Wrestling betting is weird