Matthew, from memory, never mentioned Russell's patio doors.
True - he didn't mention those patio doors, but he did say he took the 'quickest route' from Russell's apartment to the McCans, which would surely be via the patio door and down the pathway at a the back of the apartments - and not the long way round - across the car park.
Quote from his 2nd interview
That, on that occasion, Russell and he went to their own residences, to check on their own children. After leaving his apartment he went to that of Russell who opted to stay there to calm his daughter who was crying, that done with the deponent went alone to the McCann apartment. He clarifies that Russell's daughter was ill, with vomiting.
To this end, he took the quickest route between Russell's apartment and the side garden gate entrance to the rear patio of the McCann residence, to which he gained access through the glass sliding door into the apartment lounge. The door was closed but not locked as Kate had said it would be.
End quote
I can't think of any reason for him to lie - as I can't see what he would have to gain by doing that.
AIMHO