Manchester City came within six minutes of a tenth successive Premiership home win since the start of the season until Blackburn's in-form striker Roque Santa Cruz headed his seventh goal in four appearances and ensured Rovers earned a share of the spoils in a 2-2 draw.
But the Bulgarian international was instrumental in City regaining the lead when his strong run and cross forced Rovers centre back Ryan Nelsen to put through his own goal.
City failed to make their dominance pay in the second half and paid the price late on allowing the Paraguayan international a free near post header.
For a moment it seemed as if the assistant referee Darren Cann had flagged for offside against David Dunn. But referee Howard Webb awarded the goal after confirming that Cann had had a change of mind after initially raising his flag.
Asked about the situation and whether or not he thought the goal should have counted, a rather confused Eriksson told Sky Sports: "Well I don't know.
"One Blackburn player is flagged offside after trying to knock it with his head but not reaching it. Santa Cruz comes in behind and scores."
Put to him that if a player does not touch the ball he is not offside, Eriksson responded: "If that's the rule then yes, it's a goal.
"He tried to touch it but he didn't so it's a goal.
"I think it's a very grey area we're talking about, I think it needs clarification but it's the offside rule - it's always a grey area."
Speaking of the performance as a whole, the Swede added: "I am disappointed that we couldn't hold onto a lead and that we conceded on two set pieces.
"Blackburn played well though. They are a good team. I think they were better than Chelsea when they played them."