Really please answer, guys, when you talk or write to a girl in a "serious" manner, is..

[Anna S]

...that a hint to her? to leave you alone? i got this twice (or guess sometimes) with guys I find attractive, but am trying to get to know at a friendship level first. maybe it's my college and the hookup culture, but i feel like any time i wanna be friends with a guy/get to know him with NO PRESSURE they act like i'm desparate for a b/f. for instance, when i emailed one if his frat was having a party he told me in a very direct and bland way, "not tonight. hope you have a good eveining..." and when i asked another one to my formal (just b/c my real date cancelled) this guy wrote back as if he was writing to a professor, that he already had plans, but thanked me for the offer and hoped I had fun! why do they act all "proper and serious" with me? to show me they have no romantic interest and I should leave alone???