What the words near the chalk lines mean:
- Director = a person who is in charge of an activity, department, or organization - in this case, Purah who is in charge of the Hateno Ancient Tech Lab
- Famulus = an assistant or servant, especially one working for a magician or scholar - in this case, Symin who is Purah's assistant.
On top of Purah being the embodiment of creative chaos and Symin being an well-organized scientist, they also have a very different approach on science itself. If you read their journals for example, Symin's research always sounds serious and neutral, describing facts and theories without much emotion, whereas Purah's notes always sound cheerful, "cool" and hyped with a few kinda improper exclamations strewn in.
As for the pictures / drawings appearing in both Tech Labs, I think this either means that Robbie is secretly just as immature as Purah (which wouldn't really suprise me, given his behaviour) or that Purah sent him some of her drawings and he hung them up inside his lab.
Either way, I think the developers did a very good job filling the world of Breath of the Wild with neat little details that tell their own tales without being outright obvious.