I am stuck on this point, we are meant to have the girl chase us, stay aloof and not chase her by any means, but at the same time how is this different from being persistent.

For example, there is this model chick that i saw once, apparently she had a crush on me and she expressed many ioi's but after this date, i didn't hear from her. I stayed away and DHV'd from far away by her seeing me around campus always talking and walking with a girl. I sent her a flake message along the lines of stating that i want her, but coming across as needy , kind of a take it or leave it text, and she responded back saying she would like to stay in touch. Bit of brushing me off.

I don't know, this was about last month, should i try to reignite this, or would that come across as needy, and how could i ?

This is delusional, no matter what you've read, the man is always in pursuit of women that is the social script. I'm not saying that women don't ever act the role as the pursuer, but ultimately if you aren't willing to make any move in pursuit of her she will find somebody who is willing to. Women want to be pursued, to some degree, it gives them a sense of being valued, desired. A confidant man WILL pursue but won't CHASE. That is, check in with her every now and again, setup dates, treat her like a lady (e.g., chivalry) etc.. Why are you fronting, you obviously like this girl. With all your posturing she'll simply go with the next guy who seems more interested. All this talk about fearing looking 'needy' is likely coming across as disinterest to her.