Yes, I think their stick writing, when directed at us, is an attempt at communication with us. But I think they're pretty clear that we won't understand it. I think they're just saying "we're here" and trying to engage us.
I have left stick formations for them that they have then rearranged, and then I rearrange the rearrangement, and then they rearrange my rearrangement of their rearrangement, and so forth. And I haven't been killed for making spelling mistakes, or even maimed.
But I kinda got bored with the stick drawings, and I think they did, too, and we moved on to other things.
It's all just one big "hello". The details are not important. If they were, the BF would figure out another way to drive those details home, and there would be no mistaking their meaning when they did.
I don't think it's useful to worry about what you might be saying inadvertently. If you're afraid and worried when you try to communicate, that's what they'll notice: the fear and the worry. If you can relax a little about your messages, they'll notice that, too -- the relaxation -- and you'll be fine.
I've never heard of a male BF killing a male human in a fit of jealousy over a female BF, so that's another thing that's probably worth crossing off the list of things to worry about.