Just had the gate and fence, fence on one side, gate on the other side of my home. The fencing company choose to drill into my home rather that use post. I asked why they did that and they said because of drain pipes that come off the roof of my home. Is this a common practice or were they just trying to cut corners?
Unless there is something unusual about your home, normal practice is to install a post at the wall of the house. NORMAL.
Now why they did not do that on yours the roof drain just flows into where they would normally put the post .. I could see they are expecting a wood post to rot.
Other than that I think they gave you an answer; not a good answer but an answer.
No digging next to the house, no putting in a post and no labor to do all of that. Time & Money. Me personally depending on the scenario like an unusual house - my preference is Never to Drill into my house. Think about when it breaks how to fix that fence.
I put a post as close to the house as I could on a fence job, but because of the slab I was limited and it produced a gap. But! I filled the gap butt to the house with a custom cut of the existing fence panel boards, trimmed it nicely and matched the "look." The client was pleased. Attaching the fence to the house may be problematic on two fronts: the distance from the post to the house -- how long of a run was it? And, two, the fastener penetrations into the siding or brick or faux stone (or whatever product faces your home). If the run is a normal panel run supported on one side by the post and the other by "your house," the house side is encumbering the weight and the wind load. What did they fasten into? Stud framing? Masonry? What did they use as fasteners? Did they weather seal them or just screw them in? Those fasteners are now penetrations into the construction integrity of the house, subject to hydrolics, freezing, etc. If the fasteners allow water in over time, it could be a problem; you'll have to pay attention. If they did a good job, it's probably not a problem.