Well i think he's asking about the possibility that ancestral biological structures might have been very similar. Like say ancient vacuoles maybe existing on their own and using RNA as a means of building other vacuoles. The RNA strands might have been extremely simplistic by today's biological standards.

Then you have other extremely simplistic structures that originated somewhere else, using RNA as means of doing extremely simple and menial tasks. Then these proliferate and eventually come into contact with each other and by coincidence form more complex relationships as single structures over time, kind of how the mitochondria is theorized to have become a part of the cell millions of years later.

When they combine maybe it would be difficult to determine that they were two distinct lines of life because they used the same means of relaying genetic information.