Him knowing it was their apartment does not explain why he would (subconsciously) encourage a false alert. That makes no sense. Martin Grime knows that an alert in its own is not evidence. What we see happening in this case is Eddie’s alert in 5A providing a signpost to where Keela might be able to find traces of blood. This is exactly how it panned out. Forensic scientists collected human cellular material from under the tiles in the area where both dogs alerted. The DNA analysis found the human cellular material in swab 3a could have belonged to MM but the result was “inconclusive” because there was more than one contributor and the FSS was unable to separate these out. Dr Perlin however has offered his services.
Grime knew it was the McCann's apartment, that if there was going to be evidence it would likely to be in 5a and so he would have been anxious that the dogs did a more thorough search, this could have been picked up by the dog especially when called back a few times as if to say 'look again and make sure' Eddie wasn't at all bothered with the bedroom, now bearing in mind Grime said the dog could smell through concrete, I'm sure if there had been a scent he would have found it on his first search.
How can there be two contributors to a drop of blood?