The Blades won their first point on the road with a goalless draw against Posh, who would have gone top of League One for the first time this season with a victory.
Ferguson said: "You get frustrating nights like this during the course of a season.
"Sheffield United just parked the bus and I didn't think they would play like that against us. It probably goes down as a compliment to my team.
"We tried three different formations during the course of the game but couldn't get ourselves a goal.
"It is another game unbeaten and we don't look like losing matches.
"We have only dropped seven points out of 39 and that goes down as very good form.
"We are not renowned for clean sheets but keeping five in succession highlights the maturity of my squad."
Despite Ferguson's criticism, only the woodwork denied the Blades a shock success with Lyle Taylor's thundered a 20-yard blast crashing against the crossbar eight minutes before half-time.