It was a rental, of course there's going to be other folks DNA in the house. Probably quite a few, especially since they had just moved in.
I think what someone was referring to- there was a news article in the very beginning stating that Lucas' DNA was not found in the house. Many of us saw this and discussed here and elsewhere. That's why it puzzled many folks, and it caused many of us, myself included, to believe that he had disappeared before Friday night or Saturday morning. It's still causing a lot of folks to think that the landlord had the wrong day, even though both you and FindLucasAllen have confirmed this several times. To my knowledge, there was never a correction by LE or that news site about the lack of Lucas' DNA in the house. I hope this clears up where some of these posts are coming from.