That thread seems to indeed suggest that people are confusing seeing something with imagining seeing something. The point about the common inability to draw an accurate bicycle seems to prove it.

That point actually proved nothing. It demonstrated that there's a distinction between:

1. Ability to visualize

2. Accuracy of memory

3. Ability to produce technically accurate drawings

Those aren't one thing, it's a combination of things. The same commenter tried to use helicopters (a thing which people are even less familiar with in general) to bolster their point. Like I said in that thread, I've got friends who work on helicopters (engineering side) and could produce remarkable technically accurate drawings, and some friends from the same office who couldn't draw to save their lives. It says nothing about their ability to visualize and more about the accuracy of their memory and ability to draw.

The people who had trouble drawing a bicycle from memory would presumably have no problem connecting the right parts if they had a bicycle in front of them, which suggests they are not accurately visualising a bicycle.

If I read a paragraph of text and then try to write it down from memory, I would probably produce something vaguely similar but not quite exact. Maybe I would change some words or phrases with similar ones, or miss a part entirely. The better I understand the underlying idea, the closer it is likely to be to the original, but unless I reread the paragraph many times with the specific goal of memorising it, I'm unlikely to reproduce it exactly.

Same with visualising a bicycle. I've seen many bicycles and I know what parts a bicycle has and roughly how they fit together, but unless I've paid attention to the exact shape and position of each part, I could at best visualise a rough approximation of a bicycle.

I'm not aware exactly what is wrong, just as I would not be aware of what part of the paragraph I changed. But in many ways it doesn't matter, because the high-level idea is there mostly unchanged, just as with the text. The difference is that if you don't fit the parts in exactly the right way, the bicycle will not work, but I'm unlikely to completely change the paragraph by substituting a few synonyms.

This is not even getting into the jump from visualising to drawing, which would depend on my ability to draw.

Right, but accuracy with respect to reality is not the distinction between aphantasia and non-aphantasia, that's more about memory or technical knowledge than about the ability to visualize itself. Someone without aphantasia can also visualize fantastical scenes with no connection to reality, either because it is fully fantastical (dragons and dwarves) or not a real memory (imagining meeting with someone, but it hasn't happened yet for you to be able to recall). They could visualize cartoonish scenes or cel shaded scenes or animated XKCD stick figures. None of those are realistic, but they could still be visualized in detail.

I see why you’d think that but it’s not how it works for a lot of people. As others have tried to explained to those that think no one can visualize in their head, for most of us that can visualize it’s not a photograph in your head. And besides, drawing from imagination takes practice. Heck, even drawing something that is literally right in front of you takes practice.

I don't see why one can't imagine a wrong bicycle.