I am in a similar position. While I read the "spread cheeks" as extremely crude, I don't believe they were referring to an experienced real engineer or developer. There's several in disguise running around burning bridges.
Ass in seat means you get the job done and thrive off working on it until you deliver. You'd rather stay up doing sprints than work 5 hours and snack half the day.
Spread cheeks means you won't take advantage and exploit weakness of the business founder and assume they have no value or credibility so you steal the idea for yourself. (Some of these threads definitely have statements from tech peeps who openly admit to doing and wanting to do that).
Business people have a different frankness, but none of it means they don't know or respect the value of a good engineer. (I hope).
So to put it nicely for you (while I can't speak for them, only me) -
This person wants a tech co-founder that can manage and lead the tech team, seeks to solve problems while presenting solutions on how things can be done rather than just present why things can't be done, listens and achieves business objectives set by the CEO, wants to do the job, will complete the job, is present in the job and not spending all their time talking to people about other projects that have nothing to do with the current project, understands that the business comes first, doesn't undermine the team captain (CEO) in front of others, and wants and shares their own vision for growing the project but does not let that stop them from doing what needs to be done to achieve the next milestone.
In essence, a good person that is a team player that wants and will to do what their best at all times. If they see a need to build a team, they will build a team. If they can get to the first milestone without a team, they will. It's that simple.