I feel like that's either to test yuder or get informations out of him
I don't think so because even in the flashback Yuder had slept with him and he even said that his face and body was his type.
There's a lot that readers don't know at this point in time, but if you don't mind spoilers, I come in peace was correct for this specific instance. That doesn't mean that he doesn't like Yoder or his body, but remember that Kishiar is royalty and in this universe, the body is but another card to play.
Honestly kind of disappointed on the ML for asking Yuder to sleep with him. I know this is fiction but it greatly offended me that a commander would make a sexual suggestion to his subordinate when it hasn't even been that long since they know each other too. And it seemed like Yuder was also offended and when we saw that flashback he looked sad that he only wanted to sleep with him ugh ╥﹏╥.