I can only speak for myself, so to me this technique is kind of like how they did colour photographs in the 20th century [1] - taking multiple photographs from the same perspective with different filters.

For that reason, I would argue that these are 'true' photographs. Sure, things have been differently exposed, maybe some ultraviolet light has been brought into the visual spectrum; but for all intents and purposes, the light from the subject(s) hit the lens(es) at the same time and the composition is true to what actually happened.

Now, with all that being said, there are many famous photos that are actually composites [2] and what makes 'a true photograph' is still hotly debated.

Digital processing is such an integral part of modern photography that trying to decide what makes a 'true photograph' is bound to get messy.

[1] https://petapixel.com/2014/03/10/incredible-color-photograph... [2] https://www.youtube.com/watch?v=2NeyTEO_JP0