It wasn't a surprise to see lazio defeats cagliari because it is something that have always occur in the past and Cagliari have not been doing well this season, they have been struggling to gain points but still they are at the bottom of the league standings. It is very good win win for Lazio to gain the fourth position which no one can tell if they will be able to maintain the position because Juventus is not even far from Lazio with points and it is possible for Juventus to get more points to be in the fourth position.
Lazio's victory in the match against Cagliari was in line with most people's predictions. And yes, that's normal considering the difference in quality between these two teams is quite large. But in that match, I personally saw that Cagliari seemed to be starting to change into a team that had positive improvements in terms of quality of play. Just look at the number of attacks they built into the Lazio defense area. Well that's quite a lot. But fortunately Lazio's defense was still able to withstand every attack from Cagliari.
And Lazio, which is currently ranked 4th, is not in a safe position. Because there is only a 2 point difference between Lazio and Juventus who are ranked 5th. So changes in ranking can occur quickly between the two.