The Problem with Christians

[Pat Mustard]

Citation needed.

Couldn't find one so I will concede that there is insufficient evidence for the statement. Interestingly the same website you sited for there being no reference did say this;

Note:
* Interestingly, Nachmanides, in an attempt to describe how God created everything out of nothing, did suggest the universe was originally the size of a mustard seed which then expanded.
...At the briefest instant following creation all the matter of the universe was concentrated in a very small place, no larger than a grain of mustard. The matter at this time was very thin, so intangible, that it did not have real substance. It did have, however, a potential to gain substance and form and to become tangible matter. From the initial concentration of this intangible substance in its minute location, the substance expanded, expanding the universe as it did so. As the expansion progressed, a change in the substance occurred. This initially thin noncorporeal substance took on the tangible aspects of matter as we know it. From this initial act of creation, from this ethereally thin pseudosubstance, everything that has existed, or will ever exist, was, is, and will be formed.

;tldr: Ok you've got me, I've been found out putting words in people's mouths, again.

*beat*

But he did totally say what I said he said (and have just admitted to lying about) and here is how, just have to put a few more words in the man's mouth. He's long dead so nobody'll know.

Seriously, Nacmanides didn't know what he was talking about. He was trying to simplify a very complex system (the universe and its contents) into a less complex one (mustard seed becoming mustard plant*), and to be honest he failed badly, because the universe is so large and diverse, it is almost impossible to explain by analogy, especially when the analogy uses an item which is an infinitesimal part of the universe.

*While mustard seeds becoming mustard plants is far less complex than universal creation, it is suprisingly complex, so much so that I'd be pretty confident that nobody had the foggiest until a couple of centuries ago.