There isn't a logical conflict there of course, sexuality could be a social construct despite gender not being that simple, ...it just seems odd to me. I suspect that sexuality, like gender, is not that simple.
The concept of sexual orientation is a social construct. Unquestionably. It's an idea that's pretty much unique to our culture (modern western countries primarily). Other cultures throughout history had different concepts that were quite different.
The fact that different people experience sexual or romantic attraction differently, and that not everyone is simply attracted only to the opposite sex, is not a social construct. It's a fact.
So it can be both. Just like gender is both.
Add to that the fact that identity carries with it social constructs offered by society, cognitive and psychological individual factors, etc, and that this does not rule out some biological factors regarding how the individual relates to the rest of these.
So "merely" meaning to the exclusion of other factors, sure. But that doesn't mean that the social constructs might not even be at the forefront.