Regarding Latin malum: people often have the impression that the word specifically means "apple" due to a bunch of crappy Latin textbooks. It's messier though, and the video is correct - it could be used to refer to any type of fruit, although in the absence of context you'd "default" to apples. This can be shown through synchronic evidence, like Apicius 4.3.4:

4. MINUTAL MATIANUM. [...] Media coctura mala matiana purgata intrinsecs concisa tessellatim mittes. [...]
4. Matian Mince. [...] While cooking, add [to the pot] Matian fruits (=apples) that had their cores removed and cut into pieces.

If "mala" was enough to refer to apples, why is the author specifying that those need to be "mala matiana"?

Diachronic evidence shows the same. Using Portuguese for the examples:

• mala matiana "Mattius' fruit(s)" → maçã "apple"
• mala romana "Roman fruit(s)" → romã "pomegranate"

If "mala" was used exclusively for apples the first one wouldn't get an adjective, just like in Apicius' recipe book; and the later would've never popped up.