Being broadly critical of something outside of heteronormative behavior is ok. Telling somebody you don't know in a situation that you aren't familiar with tha

Being broadly critical of something outside of heteronormative behavior is ok. Telling somebody you don't know in a situation that you aren't familiar with that they aren't secure in their relationship comes off as ignorant at best. Especially since OP describes something on the more casual side of the ENM spectrum as opposed to full fledged polyamory.