Normally yes, I do not know whether this is documented or not but by experience, I can say that this is the case. At that point that if you do not want to have several cores used by parallel branches of a same workflow, better to force them to work sequentially by adding variable connexion dependencies between them to establish the sequential order at which you need them to work.
Besides this, I often check how many cores are used by every node when they are run. I use for that the ressource monitor utility in windows, as for instance here below where you can see that the -RDKit Substructure Filter- node is employing all the cores:
This allows me to optimize the use of nodes and the performance of the whole workflow based on whether they can implicitly handle parallelism or not. This is partially explained in the the following post:
Hope this helps.
Best,
Ael