For Point No. 1 - Yes, model wise it’s better to keep them intact into the one table.
For example, when we’ve a locations table, in that we’ve fields for Address, Town, City, Territoty and Country so now in this case we don’t start creating different master tables for each of the fields/category. So yes, definitely you can combine them into the one table rather than maintaining multiple tables which share the same attributes.
For Point No. 2 - I’m not sure which video you’re exactly referring to in the given post but doesn’t matter. To achieve the analysis/results, firstly designing the data model properly is always of utmost paramount importance and than the context entered into the DAX while writing the measures played a pivotal role. If your model is correctly designed but the context entered into the DAX measure is not correct than one cannot blame the design of the model. So it goes two ways.
But yes, as I said you should combine the two tables of products and merge them into one.
Note: The videos are designed from the educational perspective and to provide the insights about how one show the analysis in Power BI so once the concept is understood than we can always write and modify the DAX measures into our models as per the requirements and achieve the analysis/results.
Hoping you find this useful.
Thanks and Warm Regards,