I'd say it's off-putting for the same reason that using technically accurate biological terminology in place of sexy-talk can be off-putting. It could come off as impersonal or alien at best, and objectifying at worst.

Think of an alien in disguise saying "hello fellow humans". Technically, it's not wrong, it's just weird.

I think it's because it's mostly used by "sigma male" seing womens as objects(not sure thought, but that's what i've seen).

If you say "This female" vs. "This woman", it could be considered very rude. English is very context dependent.

Others in this thread will tell you it's only acceptable as an adjective or for animals. That's not true. Here are some non-adjective uses that most people wouldn't consider misogynistic on the surface:

• A female changing room (noun adjunct)
• Female-only spaces. (noun)
• Sorry, this shelter is only for females. (noun)
• This procedure is not recommended for females. (noun)
• Only females are eligible for this award. (noun)
• "Is the person you're going out with tonight a male or a female?" (noun, my mom said this)
• "A male character has no stats difference compared to a female." (Probably an adjective but arguably not)

That said, "I am a single man looking for a female" is pretty gross usage. Also, please note that some of these examples may be transphobic in nature.

Can you give us more context?

"Woman" is almost always preferred because it respects one's personal identity, as opposed to the compulsory status of biological sex, which is often used as a source of belittlement and/or bigotry against women. (and carries a whole plethora of baggage when people decide they get to judge someone's female-ness)

But it doesn't mean that you shouldn't generally be able to use the term "female" without causing social friction, if you have a good amount of social grace.

(its actually quite normal in fantasy/scifi circles, for example)

I think you may be asking the wrong question- you may want to explain what you were talking about and ask what specific phrases or situations might have unsettled people.

Maybe it was just a weirdly specific English faux pas, or maybe you have a friend who is a little extra sensitive after bad experiences and who could use your support. Maybe its a total miscommunication- who knows?