Neurologic coherence between numbers and colors?

I came across a magic trick on YouTube that made me curious (starting from 10m15s). Maybe it has something to do with synesthesia? But let me first describe the trick in short.

It involves two persons. One from the audience and of course the magician itself. The magician holds a card with a pyramide of numbers on it, like this:

    5
5 5
5 5 5
5 5 5 5
5 5 5 5 5


Then the magician asks the person to read out loud the numbers several times (five, fifty five, ...). The magician informs the person beforehand, that he is going to ask a question later on. And that he wants the person to answer it right away.

Then after a minute or so, the magician asks: "Think of a vegetable and tell me it's name". According to this trick there is a 70% chance that the person answers carrot. And the second most given answer is tomato.

Now, why is that? The magician explains this with a neurological coherence between numbers and colors. Would that be some form of mild synesthesia that a lot of perople have? So that (statistically seen) the neurological representation of number is similar to the perception of a specific color?

Please bear with me, I am total laymen on this topics!