There is no way for us to know that based only on the information you’ve offered. There are no standard conventions of “infography”. An"A3 page" could be hung on a wall or lain on a desk. There may be lengthy paragraphs of that 8-point type or just a few easily-digested lines.
The 8-point choice does seem rather small in a layout where the title is set at 70, but maybe the title and context of the content warrant that wide departure. Can we see it?
There are no hard and fast rules regarding minimum type sizes. Instead, it’s about legibility and readability. If the words are meant to be easily read, they need to be large enough to enable people to do so. You can use your own eyes to determine that.
Keep in mind, though, that people’s ability to focus at short distances begins to decrease in their teens. It doesn’t typically become noticeable until around the age of 40 when focusing distance finally decreases to just under normal reading distance.
In other words, if you’re 22 years old and thinking all you need to do to make something readable is to bring it closer to your face, that solution probably won’t work for a 30-something person. For those a decade older, the 9-point type that’s easily read at normal reading distance for a younger person begins to look blurry, and they start complaining about the type being too small, squinting their eyes, and holding the reading material further away from their face to focus on it.