That report came only from WSYX ABC 6 Columbus based off the 911 call (and was repeated by People etc.) It stated:
1. We don't know it's accuracy. I've heard the dental practice's 911 call but have not heard a link to this one.
2. We don't know if the friend had access into the residence/crime scene.
3. We don't know if the basement was used as say a guest bedroom and that for whatever reason is where they ended up and that's the location cited (you can see into the basement through the large egress window). I doubt this because reports of the wellness check said the officer checked both the front and back door, so he would have seen the same thing and had probable cause to immediately enter.
4. It is possible that he like
@OhioGuy suggested procured a ladder and checked the second story windows, though seems a bit more far fetched. There are actually not that many windows and the sides of the houses between are minimized for privacy. Maybe they had an extendable pole cam or a drone even, yes far-fetched but who knows?
The wedding video that they are keeping up on YT, though heartbreaking from a human perspective, provides a lot of layout from a clinical web sleuthing angle, including the inside of the house and a hovering drone shot of the entire neighborhood/back alley/yard, adjacent streets etc.