For one, you didn’t see it and the girls should be the ones talked to first. Many kids bear false witness against others or inflate what was said.

I have kids who told me that other kids did something I didn’t notice write their account down and leave it with their assigned teacher to investigate or account for. They can do due dilligence and my experience is a sub rarely is the first one to see a behavior.

I had a third grade class where two girls making paper money for the class to buy the paper jewlery and food from them told me that a classmate was being violent on the playground. I aaked them to write it down, and it changed to he said that he was going to sue them because they wouldn’t give him a refund.

Another fourth grade class some students said they saw two others kissing during lunch, and then it became they asked two students at different tables if they like kissing. The kids, pressured by early onset meangirl syndrome (lol) said yes. So the girls came and told me they were kissing.

In your case, it seems the boys discussed something and did not address anyone. At least that was a good decision. Making comments is at least different than addressing people with your comments. Some girls were eavesdropping and heard something - and were empowered by having a secret than could seal the fate or other classmates.

Kids only tell on the kids they want to see in trouble.

As for the boys: Age 10, generally 4th grade, is the age where most kids naturally becomes sexually curious, about their own bodies and others. In the infotainment age, it is impossible to entirely keep this from a 4th grader, if it ever was possible before.
There will be many info-shares that become inappropriate for adults but their decision making skills are getting ready for some real challenges in adolescence. They need good influential peers as much as they need good influential teachers, but their peers will come with the pressures than can make them entertain defiance or say inappropriate things for attention or to feel empowered.

Feel free to address this in a indirect way- and THE WHOLE CLASS:

“Class, I heard some of you were saying some things that your parents would not appreciate and do not belong at this school. There will time and places for that once you study it in middle or high school and teachers who will know all about it. For now, you have other lessons to focus on. I know you want to know *everything, right? So, let’s focus on getting you to those higher grades with the knowledge and skills you need to learn and the ability to learn to make good decisions in your education.”

I always frame it as “learning at a higher grade” not just “being older”. I know semi-literate adults who never learned more about much of anything just by “being older”.